I have been running a 2 disk software RAID-0 in my 2008 Mac Pro for years and it has survived many OS upgrades without a problem. I now am running a 2-240GB SSD RAID-0 boot/apps/user and the original 2 1TB disks RAID-0 and it has been unfazed by the recent Mountain Lion point upgrades.
As with any OS upgrade, it is good practice to have a recent TM or CCC backup before starting the upgrade.
Good luck,
-howard