Two things I'd try:
First, see if your distribution has a "manual install" selection, SuSE Enterprise does, not sure about RH. However you do it, first load the "megaraid_old" module, THEN load the megaraid module. You should then be able to see the disks. I had this same problem with another similar server here, and that got me going. One word of warning with this, is to be sure to run "mkinitrd" afterwards, after putting those modules (in that order!), into your kernel-boot config. Otherwise, you'll have to boot from CD every time, load the modules by hand, then continue to boot from hard-disk.
Another option is to try to update the BIOS/firmware on the system and controller. I've seen newer distros not be able to find older hardware, but work fine after that.
Hope this helps.