Absolutely.
pptp uses tcp/1723 for control only - the actual traffic is encapsulated in GRE.
i do it
chain=input action=accept protocol=gre log=no log-prefix=""
and this is the log
13:10:47 pptp,info TCP connection established from My real Ip
13:10:47 pptp,debug,packet rcvd Start-Control-Connection-Request from My Real Ip
13:10:47 pptp,debug,packet protocol-version=0x0100
13:10:47 pptp,debug,packet framing-capabilities=3
13:10:47 pptp,debug,packet bearer-capabilities=3
13:10:47 pptp,debug,packet maximum-channels=1
13:10:47 pptp,debug,packet firmware-revision=0
13:10:47 pptp,debug,packet host-name=anonymous
13:10:47 pptp,debug,packet vendor-name=
13:10:47 pptp,debug,packet sent Start-Control-Connection-Reply to My Real Ip
13:10:47 pptp,debug,packet protocol-version=0x0100
13:10:47 pptp,debug,packet result-code=1
13:10:47 pptp,debug,packet error-code=0
13:10:47 pptp,debug,packet framing-capabilities=2
13:10:47 pptp,debug,packet bearer-capabilities=0
13:10:47 pptp,debug,packet maximum-channels=0
13:10:47 pptp,debug,packet firmware-revision=1
13:10:47 pptp,debug,packet host-name=MikroTik
13:10:47 pptp,debug,packet vendor-name=MikroTik
13:10:47 pptp,debug,packet rcvd Outgoing-Call-Request from My Real Ip
13:10:47 pptp,debug,packet call-id=53934
13:10:47 pptp,debug,packet call-serial-number=8500
13:10:47 pptp,debug,packet minimum-bps=1000
13:10:47 pptp,debug,packet maximum-bps=100000000
13:10:47 pptp,debug,packet bearer-type=3
13:10:47 pptp,debug,packet framing-type=3
13:10:47 pptp,debug,packet packet-recv-window-size=8192
13:10:47 pptp,debug,packet packet-processing-delay=0
13:10:47 pptp,debug,packet phone-number-length=0
13:10:47 pptp,debug,packet phone-number=
13:10:47 pptp,debug,packet subaddress=
13:10:47 pptp,ppp,debug <0>: LCP lowerup
13:10:47 pptp,ppp,debug <0>: LCP open
13:10:47 pptp,debug,packet sent Outgoing-Call-Reply to My Real Ip
13:10:47 pptp,debug,packet call-id=0
13:10:47 pptp,debug,packet peers-call-id=53934
13:10:47 pptp,debug,packet result-code=1
13:10:47 pptp,debug,packet error-code=0
13:10:47 pptp,debug,packet cause-code=0
13:10:47 pptp,debug,packet connect-speed=100000
13:10:47 pptp,debug,packet packet-recv-window-size=100
13:10:47 pptp,debug,packet packet-processing-delay=0
13:10:47 pptp,debug,packet physical-channel-id=0
13:10:47 pptp,ppp,debug,packet <0>: rcvd LCP ConfReq id=0x1
13:10:47 pptp,ppp,debug,packet <mru 1400>
13:10:47 pptp,ppp,debug,packet <asyncmap 0x0>
13:10:47 pptp,ppp,debug,packet <magic 0x10580168>
13:10:47 pptp,ppp,debug,packet <pcomp>
13:10:47 pptp,ppp,debug,packet <accomp>
13:10:47 pptp,ppp,debug,packet <0>: sent LCP ConfReq id=0x1
13:10:47 pptp,ppp,debug,packet <mru 1450>
13:10:47 pptp,ppp,debug,packet <magic 0xfd4586e>
13:10:47 pptp,ppp,debug,packet <auth mschap2>
13:10:47 pptp,ppp,debug,packet <0>: sent LCP ConfRej id=0x1
13:10:47 pptp,ppp,debug,packet <asyncmap 0x0>
13:10:47 pptp,ppp,debug,packet <pcomp>
13:10:47 pptp,ppp,debug,packet <accomp>
13:10:48 pptp,ppp,debug <0>: LCP timer
13:10:48 pptp,ppp,debug,packet <0>: sent LCP ConfReq id=0x2
13:10:48 pptp,ppp,debug,packet <mru 1450>
13:10:48 pptp,ppp,debug,packet <magic 0xfd4586e>
13:10:48 pptp,ppp,debug,packet <auth mschap2>
13:10:50 pptp,ppp,debug <0>: LCP timer
13:10:50 pptp,ppp,debug,packet <0>: sent LCP ConfReq id=0x3
13:10:50 pptp,ppp,debug,packet <mru 1450>
13:10:50 pptp,ppp,debug,packet <magic 0xfd4586e>
13:10:50 pptp,ppp,debug,packet <auth mschap2>
13:10:50 pptp,ppp,debug,packet <0>: rcvd LCP ConfReq id=0x1
13:10:50 pptp,ppp,debug,packet <mru 1400>
13:10:50 pptp,ppp,debug,packet <asyncmap 0x0>
13:10:50 pptp,ppp,debug,packet <magic 0x10580168>
13:10:50 pptp,ppp,debug,packet <pcomp>
13:10:50 pptp,ppp,debug,packet <accomp>
13:10:50 pptp,ppp,debug,packet <0>: sent LCP ConfRej id=0x1
13:10:50 pptp,ppp,debug,packet <asyncmap 0x0>
13:10:50 pptp,ppp,debug,packet <pcomp>
13:10:50 pptp,ppp,debug,packet <accomp>
13:10:52 pptp,ppp,debug <0>: LCP timer
13:10:52 pptp,ppp,debug,packet <0>: sent LCP ConfReq id=0x4
13:10:52 pptp,ppp,debug,packet <mru 1450>
13:10:52 pptp,ppp,debug,packet <magic 0xfd4586e>
13:10:52 pptp,ppp,debug,packet <auth mschap2>
13:10:53 pptp,ppp,debug,packet <0>: rcvd LCP ConfReq id=0x1
13:10:53 pptp,ppp,debug,packet <mru 1400>
13:10:53 pptp,ppp,debug,packet <asyncmap 0x0>
13:10:53 pptp,ppp,debug,packet <magic 0x10580168>
13:10:53 pptp,ppp,debug,packet <pcomp>
13:10:53 pptp,ppp,debug,packet <accomp>
13:10:53 pptp,ppp,debug,packet <0>: sent LCP ConfRej id=0x1
13:10:53 pptp,ppp,debug,packet <asyncmap 0x0>
13:10:53 pptp,ppp,debug,packet <pcomp>
13:10:53 pptp,ppp,debug,packet <accomp>
13:10:56 pptp,ppp,debug <0>: LCP timer
13:10:56 pptp,ppp,debug,packet <0>: sent LCP ConfReq id=0x5
13:10:56 pptp,ppp,debug,packet <mru 1450>
13:10:56 pptp,ppp,debug,packet <magic 0xfd4586e>
13:10:56 pptp,ppp,debug,packet <auth mschap2>
13:10:56 pptp,ppp,debug,packet <0>: rcvd LCP ConfReq id=0x1
13:10:56 pptp,ppp,debug,packet <mru 1400>
13:10:56 pptp,ppp,debug,packet <asyncmap 0x0>
13:10:56 pptp,ppp,debug,packet <magic 0x10580168>
13:10:56 pptp,ppp,debug,packet <pcomp>
13:10:56 pptp,ppp,debug,packet <accomp>
13:10:56 pptp,ppp,debug,packet <0>: sent LCP ConfRej id=0x1
13:10:56 pptp,ppp,debug,packet <asyncmap 0x0>
13:10:56 pptp,ppp,debug,packet <pcomp>
13:10:56 pptp,ppp,debug,packet <accomp>
13:10:59 pptp,ppp,debug,packet <0>: rcvd LCP ConfReq id=0x1
13:10:59 pptp,ppp,debug,packet <mru 1400>
13:10:59 pptp,ppp,debug,packet <asyncmap 0x0>
13:10:59 pptp,ppp,debug,packet <magic 0x10580168>
13:10:59 pptp,ppp,debug,packet <pcomp>
13:10:59 pptp,ppp,debug,packet <accomp>
13:10:59 pptp,ppp,debug,packet <0>: sent LCP ConfRej id=0x1
13:10:59 pptp,ppp,debug,packet <asyncmap 0x0>
13:10:59 pptp,ppp,debug,packet <pcomp>
13:10:59 pptp,ppp,debug,packet <accomp>
13:11:01 pptp,ppp,debug <0>: LCP timer
13:11:01 pptp,ppp,debug,packet <0>: sent LCP ConfReq id=0x6
13:11:01 pptp,ppp,debug,packet <mru 1450>
13:11:01 pptp,ppp,debug,packet <magic 0xfd4586e>
13:11:01 pptp,ppp,debug,packet <auth mschap2>
13:11:02 pptp,ppp,debug,packet <0>: rcvd LCP ConfReq id=0x1
13:11:02 pptp,ppp,debug,packet <mru 1400>
13:11:02 pptp,ppp,debug,packet <asyncmap 0x0>
13:11:02 pptp,ppp,debug,packet <magic 0x10580168>
13:11:02 pptp,ppp,debug,packet <pcomp>
13:11:02 pptp,ppp,debug,packet <accomp>
13:11:02 pptp,ppp,debug,packet <0>: sent LCP ConfRej id=0x1
13:11:02 pptp,ppp,debug,packet <asyncmap 0x0>
13:11:02 pptp,ppp,debug,packet <pcomp>
13:11:02 pptp,ppp,debug,packet <accomp>
13:11:05 pptp,ppp,debug,packet <0>: rcvd LCP ConfReq id=0x1
13:11:05 pptp,ppp,debug,packet <mru 1400>
13:11:05 pptp,ppp,debug,packet <asyncmap 0x0>
13:11:05 pptp,ppp,debug,packet <magic 0x10580168>
13:11:05 pptp,ppp,debug,packet <pcomp>
13:11:05 pptp,ppp,debug,packet <accomp>
13:11:05 pptp,ppp,debug,packet <0>: sent LCP ConfRej id=0x1
13:11:05 pptp,ppp,debug,packet <asyncmap 0x0>
13:11:05 pptp,ppp,debug,packet <pcomp>
13:11:05 pptp,ppp,debug,packet <accomp>
13:11:08 pptp,ppp,debug,packet <0>: rcvd LCP ConfReq id=0x1
13:11:08 pptp,ppp,debug,packet <mru 1400>
13:11:08 pptp,ppp,debug,packet <asyncmap 0x0>
13:11:08 pptp,ppp,debug,packet <magic 0x10580168>
13:11:08 pptp,ppp,debug,packet <pcomp>
13:11:08 pptp,ppp,debug,packet <accomp>
13:11:08 pptp,ppp,debug,packet <0>: sent LCP ConfRej id=0x1
13:11:08 pptp,ppp,debug,packet <asyncmap 0x0>
13:11:08 pptp,ppp,debug,packet <pcomp>
13:11:08 pptp,ppp,debug,packet <accomp>
13:11:09 pptp,ppp,debug <0>: LCP timer
13:11:09 pptp,ppp,debug,packet <0>: sent LCP ConfReq id=0x7
13:11:09 pptp,ppp,debug,packet <mru 1450>
13:11:09 pptp,ppp,debug,packet <magic 0xfd4586e>
13:11:09 pptp,ppp,debug,packet <auth mschap2>
13:11:11 pptp,ppp,debug,packet <0>: rcvd LCP ConfReq id=0x1
13:11:11 pptp,ppp,debug,packet <mru 1400>
13:11:11 pptp,ppp,debug,packet <asyncmap 0x0>
13:11:11 pptp,ppp,debug,packet <magic 0x10580168>
13:11:11 pptp,ppp,debug,packet <pcomp>
13:11:11 pptp,ppp,debug,packet <accomp>
13:11:11 pptp,ppp,debug,packet <0>: sent LCP ConfRej id=0x1
13:11:11 pptp,ppp,debug,packet <asyncmap 0x0>
13:11:11 pptp,ppp,debug,packet <pcomp>
13:11:11 pptp,ppp,debug,packet <accomp>
13:11:14 pptp,ppp,debug,packet <0>: rcvd LCP ConfReq id=0x1
13:11:14 pptp,ppp,debug,packet <mru 1400>
13:11:14 pptp,ppp,debug,packet <asyncmap 0x0>
13:11:14 pptp,ppp,debug,packet <magic 0x10580168>
13:11:14 pptp,ppp,debug,packet <pcomp>
13:11:14 pptp,ppp,debug,packet <accomp>
13:11:14 pptp,ppp,debug,packet <0>: sent LCP ConfRej id=0x1
13:11:14 pptp,ppp,debug,packet <asyncmap 0x0>
13:11:14 pptp,ppp,debug,packet <pcomp>
13:11:14 pptp,ppp,debug,packet <accomp>
13:11:17 pptp,ppp,debug <0>: LCP lowerdown
13:11:17 pptp,ppp,debug <0>: LCP lowerdown
13:11:17 pptp,ppp,debug <0>: LCP down event in starting state
13