OK ONE MORE THING,
Is this actually the same device, rmt0 and mt0?

The one time I tried to do this, I found that I couldn't use the 8mm drive
for ADSM ( this was a LONG time ago, so I don't remember exactly) and for
AIX, at the same time.  I had to make the rmt0 driver UNAVAILBLE to AIX,
before ADSM was able to use the drive as mt0.  At least that's what I
remember.

I don't remember whether I went into SMIT and found a way to make it
UNAVAILBLE, or I just DELETED it.
(Don't worry, it will come back when you run cfgmgr).
This was a LONG time ago, so it may not be the problem at all.

Now that's the end, I'm giving up, not saying another thing.