How good do you think your Disaster Recovery procedure is?  Have you tested
it before?  If you have that under control then you should be able to answer
your own question here.  The issue is you need to have all your software to
reinstall the TSM server from scratch if something goes disarray.  Perform a
DR backup right before the microcode update.  Examples of things to do:

        Backup all your storage pools to copy pools
        Do a Database Snapshot to tape of your TSM Database (2) if you are
not comfortable.
        List off your file system structure
        Do a DEVCONFIG and VOLHISTORY backup and print or copy to a
removable media.
        Determine the maintenance level for everything.
        Make sure you have all the media to build the TSM server from
scratch (tapes or CDs).
        mksysb is the best way to go.

If you have all these things (there may be others) you have the equivalent
of cardiac arrest paddles to jumpstart your TSM server and restore the
environment once any hardware problems introduced by the upgrade are
resolved.

Also, pin down the microcode update and make sure no software prerequisites
are necessary for AIX and your release of TSM.