[@Akayaofthemoon] I could see Garnet just watching everyone while they interact, occasionally speaking. Amethyst would probably hang out with Wendy or Soos (I'm guessing), while Pearl would speak with Dipper and Ford. 

Stan: Come one and all! And see the freaks from outer space, The Rocklings! Fifteen buck per view! *takes money from customers*

[@pyroman] I bet Dipper would be overly cautious of the gem monsters, and trying to find anything he can about the Gem aliens in the journals. 
I think he may pretend he never saw fusion dances if any of the gems decided to fuse.