You have to create mt0 in 'smit-devices-ADSM devices' (AIX anyway)then you
have to disable rmt0 but leave the definition in place (rmdev -l rmt0).
While ADSM has the 'mt0' device Available, you won't be able to use 'rmt0'
unless you do the following commands:

rmdev -l mt0
mkdev -l rmt0

Not a good idea to switch between the two too much.  But if all you need is
to do a 'mksysb' now and then this will work.