This is my preferred way to manage DB2 on CMOD servers.
TSM has three core functions: Backup, Archive, and Hierarchical Storage Management ("HSM") -- and it's great at all of them.
Interestingly enough, using the TSM API to back up DB2 is configured as an archive instance -- so there's no change in thinking required.
As far as I know, the usage of TSM in this fashion is permitted as long as you aren't using devices that require additional licensing in TSM.
Of course, this also means that you absolutely must ensure that your TSM server and data can be restored in the event of a TSM issue -- because you could end up losing both the CMOD database, and the CMOD data.
-JD.