Wouldn't the monkeys fight eachother over who gets the banana first? I mean you have both punishment and positive reinforcement. I'd say that (also depending on how well they are fed), the monkeys wouldn't just try to prevent the others from getting it, but would want to get it themselves. Monkeys don't seem to strike me as being creatures who have surpassed the first moral stage. (
Kohlberg's stages of moral development - Wikipedia, the free encyclopedia)