If I wanted to put a mikrotik at a customers house and they also had their router, if I put the public IP in my router (via PPPoE or some method) and then NATed all traffic to their router wan IP (static or whatever) both src-nat and dst-nat, If they put a port forward in there router, it would nat properly out the public IP Correctly?

In theory I figure it will but I thought I would get some other opinions. I will probably be testing it.