Gambling is everywhere, so I didn't get shocked if there's gambling in prison even though it's prohibited.
Even with recreational activities like sports, weightlifting, or board games, they can still bet without their warden knowing.
The prison world is an entirely different environment and has got its own laws, haven’t been there but I know this for sure and gambling wouldn’t be a very odd practice there. Once you are the type that gambles, you would find a way to participate in the activity even in places where you haven’t got freedom. Prohibited… they don’t get to announce that they are gambling and might not put out stakes to be readily visible so long as they could agree and its game on.
If it’s ideal, I can’t say, it’s left for those in prison to say what they get from the activity but, it wouldn’t be a bad way to while away the time.