No idea about your NT problem.  I've seen this myself, but never resolved
it.

The best way to build off-site volumes is by using a copy storage pool
(tape) and the backup stg command.

Yes, you should probably back up ADSM as described in the ADMIN guide.  I
would think it will be easier to recover ADSM using their procedure than
the AS/400 procedure.  I'm not an AS/400 guy though.

On a daily basis you should backup your storage pools, backup your database
and make sure a copy of the volhist.out and devconfig.out files are off of
your server.  You need those two files and a good database backup to
restore and ADSM server.  You need a copy of the client data (backup stg
into a copy storage pool) to finish the restoration job.

Kelly