Have you installed the Atape driver needed for LTO tape drive support on AIX?
lslpp -hac | grep -i atape
should find it.
Even without the driver I would expect AIX to configure the drive as "other scsi tape drive" or something similar.
The tape device will be rmt0 not mrt0 as shown in your last post.
Have you terminated the scsi bus correctly?
What does '# lscfg -vp l grep -i -p rmt' and '# lsdev -Cc tape' show?
This gives Atape info as well as links to download the latest Atape driver:
IBM - Upgrading Atape device driver in AIX