1. make a BACK-UP or clone (CCC) of the raid to external hdd
2. move the disks to new MP
3. format (and partition) the array
4. clean install OS
5. migrate all current users/settings/progs
You can probably do it non-destructively if you have the Mac Pro RAID Card, and you move the card into the new machine along with the drives. I doubt you have that, though (it was very expensive).
RAID arrays, in general, are not transplantable into different hardware.
if software RAID and data only, you can plug those into any mac (via an enclosure with the nMP) and they will be recognized.
if it's the OS, there are potential compatibility issues if attempting to boot from it. e.g., they might have 10.6 on them, which would not be compatible with the nMP.
no matter what, you should be able to read the drives.