I don’t think there is a connection between the game and intelligence) I think any game is more about skills and understanding the rules of the game, first of all, the better a person knows them and understands how his opponent plays, then he will play better accordingly.
He wont play better, he will have a better understanding of the rules, but knowing them does not give the player any sort of edge over the casino.
Whether poker players and all have higher intelligence? No, they are skilled but if they were so intelligent, they would be doing something else and working on something huge than sit on a table with cards.
However those who regularly play games like slots, I tend to have a feel that they are somewhat getting demented with time. Though I might be completely wrong.