I always tip the dealers when i play craps, especially if I have a winning session. I don’t think that it affects the game in any way, but is nice to give the dealers a little addition to their low wages. When I tip, I just throw a chip on the felt and say “for the dealer”. The dealers have a tough job and they often have to deal with a noisy crowd of gamblers. I like to show that I appreciate their terrific work.
Some players like to put a craps bet for the dealers instead of giving just a chip, and they usually put it in the middle section of the table. Most players know that the bets in that area are a sucker bets with a big house edge. If you tip with a bet you will just give the house an advantage on that money, and why would you want that. The craps dealers are of course familiar with the game and most of them know what a bad bet is. It is more appreciated to just hand over a chip. In the long run that is better for everybody.