So my question is, is the percentage of the rich gambling lower than the middle and lower class?
It depends how you look at it really and there is a pretty huge spectrum to cover. Those who have little money will either be a problem gambler spending all their spare funds or someone that is just doing it for a bit of social fun, not expecting a big win realistically - just hopeful. The same goes for the rich, who can get caught up in the same psychological and addictive behaviors, they just have a much longer trajectory until they fail. Sometimes it doesn't even take long for the rich to become poor as they are liable to just drop down bigger number bets than others. Gambling when you have little money is going to make you even more depressed when it inevitably fails.
Gamblers that use gambling for pressure are few and these are the set of gamblers that are enjoying gambling because they don't chase their losses and they always know when to stop the game. This is why it is not because of insufficient funds that is making a poor man to gamble. Your are poor those not mean that you are not happy and cannot have fun.