Tested the one internal 1g jaz drive as an external setup with an ATX power supply and a ribbon-to-din adapter. My Mac SE/30 properly recognized the drive and its SCSI ID (6) and even recognized that there was a disk inserted! SCSIprobe didn't report any SCSI termination issues and my other SCSI devices were working fine (I had a zip drive connected on ID 5, and no, it was not terminating the chain, the terminator switch was off on the zip drive).
But that's where the good news stopped. It did a lot of clicking, eventually it would say the disk needed initialized. When I tried to initialize it, it would mess about for a bit and then come back with the CD icon and tell me the disk was write protected. I know for a fact it is not write protected, as I had used the disk in my 2g external jaz drive successfully. I tried other disks, I tried removing the CD driver (extension), thinking maybe it was interfering with the iomega driver. But it was not. Among my many attempts, I even tried it without the disk inserted and it would recognize the drive. Due to the clicking (is that click of death? is that even a jaz drive thing, as I thought that was a zip drive thing?!?) and the refusal to see the disk as writable means something is wrong with the drive. As far as I understand, jaz drives can be write protected using the jaz tools software, but I don't have anything with that software running. Also, the disk was writable in my 2g jaz drive, so I think it is this drive.
I'll uninstall the other internal jaz drive for testing later. I'm not expecting it to work either.
On the good side, I discovered an old IBM SCSI CDROM drive that I bought a while back while I was looking for an adapter. The drive works like a charm with my SE/30 and it is dead silent when running (not like some of the later drives that sounded like aircraft taking off). So... yay!?!