I found a guide through Google for Backup Strategies and found that Cisco recommend Veritas BackupExec.
Has anyone any idea if IBM Tivoli Storage Manager would be a "supported" backup solution, and if so are there any caveats we might need to be aware of?
I agree with you that even today you would find links on cisco.com which would list Veritas as a supported backup utility. When you scroll down to the end of this page, it shows "Posted: Sat Sep 28 01:52:25 PDT 2002". I dont believe this link was every updated over the years.
As of now, The Unity BU does not test any 3rd party Backup Utility. They only test DiRT with Unity and therefore only that is "Officially Supported". If you wish to use the 3rd Party Backup utility, I'd recommend using it on a Lab Server before you install it in Production system to ensure that it does not affect Unity.