Don't remember from reading the book if Spilotro had a poker cheating operation going in real life, but in the movie's universe, Nicky had his crew in there playing poker and using signals to team up on other players, which is a no-no. The cowboy was obviously part of that crew but at the time he was kicked out he was probably just playing blackjack and drinking.
"...the successful annihilation of organized crime's subculture in America would rock the 'legitimate' world's foundation, which would ultimately force fundamental social changes and redistributions of wealth and power in this country. Meyer Lansky's dream was to bond the two worlds together so that one could not survive without the other." - Dan E. Moldea
