I have a Mac Pro with 3 physical disks. Disk 1 is my system, and 2 & 3 are my Data RAID. If I do a clean install of Leopard, and I try to (re) create my RAID, will it wipe out everything on those disks or will it leave the data intact?
If you do a clean install on Disk 1 it will not wipe the array formed by 2 & 3. Recreating the RAID would wipe it, but there should be no reason to recreate the array.
Don't recreate the RAID, just leave it alone and it will 'just work' as it is with the data intact. If you rebuild the RAID in the installer disk utility then it'll probably trash the data on the volume.