In Vegas when Moe walks in the room he says, "Hey, everybody's here! Tom! Good to see you Mike." Tom not only doesn't seem to shake his hand it seems he doesn't even acknowledge Moe. Granted the scene is shot in a way that makes it difficult to see but if Tom did give Moe the snub was it because he knew it was about to get ugly?

Tom's taciturn disposition is evident throughout I & II. It didn't have anything to do with Moe.

I thought I detected a look of disgust or disapprobation on Tom's face. I'm guessing he anticipated that Moe wouldn't want to sell, and would be bombastic and abusive about it.

TB, don't forget that by that scene Tom had already been removed as Consigliere. That, combined with his generally taciturn disposition (as I characterized him above)would account for a perceived displeasure with Moe. Remember also that in response to Fredo's appeal to him to intervene with the Don on Moe's behalf, that he rather irritatingly tells Fredo that Mike is in charge of the family business. Tom was already in a disgruntled mood.

True enough. But it raises another point:

Michael was confident that Moe would go for his deal. He tells Fredo that "Moe Green will sell us his interest in the hotel," and when Fredo questions it, Michael says, "I'll make him an offer he can't refuse." Shades of Vito! Except Michael wasn't Vito at that point, and Moe did refuse. So, Fredo and Tom were right.

Though Tom had been removed as consigliere at that point, he was still acting as Michael's lawyer, and could have anticipated Moe's reaction. Good characterization of a competent lawyer: realistic assessment of the situation despite the client's (Michael's) unrealistic optimism.

Tom already knew that Moe would not sell the Casino, but came to the meeting as Michael's lawyer. He knew what would most likely happen and did in fact anticipated what Green would do. Tom did seem to be in a bad mode.