what tape drives are supported by Leap 15?

I would assume all common drives up to LTO-8. It seemed to me that SLE was better for tape drives than RHEL.
At least in RHEL, one could try “mt densities” command which gave you a list of drives that the particular version knew about.
But Suse (and Debian) have different flavour of mt that doesn’t offer densities function.

I don’t have a definitive answer here, but attached scsci devices should at least be enumerated with

lsscsi

or

cat /proc/scsi/scsi

The st kernel module provides support for many SCSCI tape drive devices. From ‘man st’…

DESCRIPTION
The st driver provides the interface to a variety of SCSI tape devices. Currently, the driver takes control of all detected devices of type “sequential-access”. The st driver
uses major device number 9.

The ‘hwinfo’ command will enumerate any connected sequential storage device…

/usr/sbin/hwinfo --tape