Yes, TSM DB restore is the same no matter if you are restoring from disk or
tape.

If you rely on TSM to restore the DB itself, it looks in the volhistory file
to find the last good DB backup.
It will see the pointer in volhistory to the disk file and use it.
(I recommend you put a copy of devconfig and volhistory in your rootvg,
also.)

If you specify yourself which "volume" TSM uses for the DB restore, you just
give it the name of the file.

It all works.