It could probably work with Bitcoin as long as the machine is online to resolve the results of play at the end of the session (as long as it wants to output the results of play as a single transaction), using the Satoshi Dice method of using the player's input transactions to construct the output where any coins won would depend on the player's coins not being double spent. (note: there's probably better ways to do this)
With the pervasiveness of wireless data connectivity and the assumption a cryptocoin operated gaming or vending machine would be permanent enough to maybe merit a wired connection, there are probably a sufficient number of ways to allow for relatively safe zero-confirmation transactions. Making sure payments include a fee, broadcasting outbound transactions only while peering with well connected vendor controlled nodes, selling Coca-Cola and not Cristal, etc.