Most likely those professional gamblers are the one who spend more time in gambling and gamble is part of their lives now. So living away from it is not easy particularly to those make it as profession because this activity by which one regularly makes a living. They badly need help especially those have symptom of addiction, they cannot do it by themselves. It take long to time before they can get over from it.
When they have good skills in specific gambling games, I think they can make a living from gambling because they will be able to get the winning from the games. But as you said, it will be still difficult for him to get the win since gambling will not only depend on the skills, but I think he will know when he can gamble and when he needs to break for a while. I think he can handle himself when he plays gambling so he can prevent the addiction because that can make him get trouble if he gets addicted.