I was having a similar problem last night and did some research and found one thing that will probably not sound too good to you, but have to share it anyways. 🙁 It indicated that an existing RAID set would not be recognized as a valid RAID set if it were hooked up to any other model of RAID controller (i.e. Oxford 912, 922 etc.) than it was when it was originally created.
If your drives are in cases (or internally mounted) with a different controller than the original RAID was created with, it seems that that might well be your problem. In my situation I had a similar dual-drive case with RAID 1 (mirrored) set up and one drive died, so in order to determine which one the dead one was I had remounted them in two single drive cases, but while they showed up as RAID slices in Disk Utility, neither could be accessed (and in short time they caused a Kernal Panic) and a new RAID set could not be created with them.
SO- back into the original case and bingo- showed the RAID with a degraded slice. Pulled one drive (naturally the wrong one), then the other and replaced the dead drive and it went about its business rebuilding the new drive with the contents of the other (which of course would not be possible with a RAID 0).