Hi,
Ubuntu is debian based. Although you can install rpm on it, dependency hell is what you can encounter. I saw a post here someone was able to run the server on Debian, so it is possible with some effort (since the TSM device drivers use native scsi passthrough driver you can make it work even with tape library - was not possible in pre-5.3 days with binary kernel-level-dependent drivers).
BUT it is considered unsupported so I would not run it in production.
And for testing purposes? Why don't you use CEntOS or other RH clone?
Harry