I'm not sure that a gambler can believe in God, because gambling is a game of chance.
However, if one who gambles became a believer in the God of Abraham, Isaac and Jacob and grew strong in faith, she/he would no longer be a gambler, because she/he would become a new creation with a renewed spirit and soul.
His divine power would give her/him everything needed for life and godliness through their knowledge of Him who has given of His great and precious promises, so that through these promises she/he can participate in the divine nature and escape the corruption in the world caused by evil desires.
A promise calls things that are not yet, as though they are. By having faith in knowing those promises will manifest themselves, because the Lord God is faithful and true. No longer would there be a need for games of chance, because she/he will always have a sure bet.