This really depends on the person, but mostly if the person's reason for converting to another religion is very personal and for his belief, for sure he can quit gambling on it as it has a spiritual effect on him as well as his belief, but again, there are still others who will play secretly.
If am looking from your perspective, you might be right, if a person convert to another religion, he won't really want to go against what the religion is against, but it might also be just temporary, with time if the person is really a addicted gambler he might end up going back to gambling, even if he will be doing it privately so that people won't know he is gambling. I think that's what most people are doing now, they are gambling secretly so that no one will know they are gambler.
I do have a lot of friends who believe gambling, drinking alcoholic drinks, and eating pig is a sin for them, but they still do it anyway, but secretly. I also have friends who really don't do it at all. But the chances really are high for those who quit gambling due to a belief or other reason.
All of those things which you mentioned is against my relegion, but people still do it. It's easier to be caught when drinking alcohol compare to when gambling, when you are drunk you might endup misbehaving, which will make people notice easily that you are drunk. But as a gamber, you can be gambling secretly and nobody will know you are gambling only if you expose yourself.