I've never seen it work without an atapi.device either.
Edit: but... I just tried (with the correct emergency disk this time) and it worked. I'm using OS3.9 CacheCDFS with SCSI.DEVICE unit 0 for my DVD/CD-RW combo. Hmm, odd. I've never had this system at 3.1 so I can't comment about the 3.1 driver.