I just installed the 2.0 Closed Beta, and for Uplay games which I bought on Steam, my play times as tracked by both are being added together, essentially doubling my total play time.

I'd think that since all Uplay games bought through Steam are launched via Uplay, Steam play times for Uplay games should be ignored?

same here. My Ubisoft Steam games are being doubled regarding play time

In some way this behaviour seems logical to me. It is the same game so one could actually say that you played it for 86 hours. And if you want to know where these playtimes exactly come from you can see it when you move the mouse over the game.
However, I do not use the community integrations so maybe you mean something else that I don't understand right now?

If you point the cursor over the total time it uses to show the times differentiated by platform as a popup.
But the standard visual showing of time is combined, indeed.

Yeah, the play times are not actually separate times I played the game - they are two representations of the same playtime/sessions, since Steams logs playtime, but Ubisoft games bought via Steam actually launch via the Uplay app, and the Uplay time is also tracked. So combing the play times makes no sense in this specific case.

There should likely be some exceptions built-in to account for this multi-launcher behaviour.

Can confirm that behavior.