The place where virtual makes sense is if you need a lot of tape
drives/tapes and the tape fill is less than 50%.  TSM generally fills tapes
up.  The issues with DR below are always a consideration.  "Appropriate" is
the key word.

The case that I can think of is when the VTS and VSM can support SAN managed
tape.  Under that scenario you may start thinking about onsite backup sets
or something like that as an example to use VTS/VSM for.  The reality is VTS
runs ADSM under the covers, at least that is what the tape drives say.

Unless some major benefit can be achieved carefully consider what you are
doing and why.