I've only had a couple of Y aeroplan flights, but both times I didn't have any issue with A3*G benefits (priority check-in/lounge). I didn't bother getting them to input my *G number on the BP since the card itself did the trick.

Interestingly enough, I had an aeroplan reward flight in F a few months ago and upon checking in with LH, the agent requested my FF card so it could be entered into the system. Since I don't have status with AC, I gave her my A3 card since I'd rather have it noted in the system that I'm *G than not.