>According to the manual, the device name needs to be /dev/mt0, not /dev/rmt0

In the manuals, they describe going through SMIT to establish the ADSM-specific
device that is needed.  ADSM has its own category for tape devices, which it
put into SMIT during ADSM installation.
Be aware that it's not *always* the case that ADSM needs an mt0 device: for
3494 libraries and 3590 drives it uses rmt0 and so forth.  You find out if
your configuration is correct when you run dsmlabel and it is either happy
with the drive or isn't.            Richard Sims, Boston University OIT