Thanks for the note, Chris.
Basic stuff may work, but advanced functionality will definitely be impacted because of a few major changes in vSphere 6.5 "under the hood". It really is NOT a dot release from this perspective. For starters, it has the new VMFS version with what it seems to be very different internals (not just some minor changes and tweaks).
So, it would be wise not treat vSphere 6.5 as a minor release from the upgrade perspective. Even the fact that it took well over 1.5 years to release kind of hints that
We're planning to support vSphere 6.5 in Veeam Backup & Replication 9.5 Update 1. As far as timelines for the latter, historically we needed on average 2 months after vSphere GA.