I think Moe knows generally what's going on. He already talked to Barzini about financing, so he must know that the Corleone financing is at risk. My guess is that he doesn't expect things to go immediately to talk of a buyout, and loses his temper.

One question I would have is: would the Corleones have pushed him out if he hadn't been skimming? My guess is that if Moe had been paying the Corleones their full share, Vito wouldn't have allowed the Corleones to go to war with him.