We are using 9.0.835 client on OS X Yosemite and it seems to work just fine even though it is not officially supported. We have over 400 Yosemite clients in our environment right now.
Anything greater than version 9 should work on Yosemite just fine. It can take IBM quite a long time to list a new version of OS X as officially supported due to being conservative about it, but we always test machines running the beta builds of OS X with not the newest client and we don’t see issues often. We typically have about 50 machines running the latest OS X within weeks of the release date running whatever version of BigFix we happen to be using at the time.
We do have one issue with Yosemite that we are aware of, but it affects a very small minority of Yosemite endpoints, and we are not entirely certain if it is a BES Client issue or something else. See that post here: OS X Yosemite (10.10) 13FileItemError