Can I install/upgrade from SL to Lion on RAID0?
I think you should be fine. I upgraded to Lion on a Mac Pro that has a RAID 0. While the OS is installed to an SSD, not RAID, Lion still detected the RAID just fine. That's obviously a different scenario than what you have, but as the software RAID is handled at a higher level than the OS, I think you should be fine.

Obviously, have a backup ready to go just in case, but my guess is that your upgrade should go smoothly.