Quandry: Do I add a backup role to my ansible stuff or not? On the one hand, backup everything. On the other - these are cattle right?

Back up enough of the data that when combined with the ansible role you can completely rebuild a machine.

It's a cow right? I need nothing more than the ansible to rebuild it? It gets its configs/data from a backed up system already.

If you can recreate it entirely from ansible without needing any external data, you don't need to back it up :)

At work we have an ansible role that lets us specify paths that need to be backed up for less cattley boxes.