It could be that the drive came formatted with non-Apple drivers. It seems to me that a SCSI drive is just a SCSI drive, nothing special besides the included driver.

To format it to Apple drivers, try a hacked HDSC Setup program. It is available here:

http://home.earthlink.net/~gamba2/hd.html

Try the one where it says "Apple HD SC Setup v7.3.5 (Patched)".

If that fails, try the 3.0.1 below on that page as well. I'd say if these utilities fail, the drive is likely to be bad, but you can easily open the enclosure and substitute any other SCSI drive.