FR runs the Apache web server on Linux.
Of course, you can run Linux on an Apple server. But you can also run it on any good quality server. So, no reason to shell out any extra $$ on hardware if all you're going to do is wipe the disk and install Linux.
As for resistance to hacking attacks, that would depend on Linux, Apache, and John and Jim's attention to the details and not on Mac OS, since it's not running in either case.
...Ah Linux, heard goods things about it. For a platform it is a rare bird but for those who have it, it does its job.
Just did a quick search on what Linux and it is a form of unix. Macintosh OSX which I am using, the tiger is unix based. It is suppose to be stable.