Mon Jun 29, 2015 12:00 am
RouterOS is a closed source piece of software, so no one (other than the developers) can know for sure, but I'm guessing...
Other than the Linux kernel, almost everything is used as a library (in the "included C code" sense), and not as a "custom UI on top". Therefore, unless the Linux program in question can be used as a library, it's unfair to say that anything is being done "through" said Linux program. One example where a project is indeed used by RouterOS in the library sense is OpenSSL, for all crypto related stuff supported by RouterOS.
AFAIK, the Linux kernel contains network filtering functionality, but it's up to programs to leverage it in order to make it useful. IPtables is merely the simplest, and therefore the most popular way to configure the kernel in most Linux distributions. RouterOS has its own implementation, which happens to be very close to IPtables in the functionality it allows the user to do.
So strictly speaking, both filters work through the Linux kernel, but are configured by two separate RouterOS subprograms (the firewall and the service manager).
As for which one is safer... They're equally safer for the "IP whitelist" scenario, but like I said, other scenarios require the use of the firewall. Those other features, if used correctly, are likely to ultimately make your router more secure, so with those in the mix, the firewall is not only the better, but in fact the only way.