2. Red Hat is not the most OS X friendly Linux. Ubuntu may be a better choice unless using Red Hat is essential for some reason.
If you also plan to dual boot OS X and Linux, then I'd suggest you create two partitions with OS X on the first partition. Then use a LiveCD version of the Linux to install it on the second partition. Some of these installations will automatically configure 'grub' with a boot menu from which you can choose to boot OS X or Linux. Some don't so you have to do some tweaking of 'grub' for the boot menu.
Alternatively, you can install rEFIt after installing Linux and OS X - CNet Downloads or MacUpdate. It provides a new OS X boot manager enabling the system choice at startup.
You'll have the best luck posting on linux forum like Ubuntu but it should work, just be sure it supports dual Xeon 5600s and such (and would be comparable to say EVGA's SR-2 or any Intel reference Skulltrail 2 board).
I have more experience with SuSE, not RHEL.
Also, maybe you would be best served with a PC and 6-core 3.33GHz Mac Pro or something else.
Would this be running only natively? or want to run under Mac OS as a guest? Parallels 6 should handle RH very well.
I have used Suse, Debian, Ubuntu. Some people do a Linux or Windows only on MacBook Pro and other models.
I would not put linux or Windows on the same drive as OS X, give them each their own, lets you do more and not have to worry about OS X Recovery partition tables.
Asking if you can do (Suse etc) struck me as... do you need to ask? maybe not for you or not ready, there is more on your own and less of that "Hand holdling" of course.