In the end, it is clear that if there is absolutely no problem or commotion caused by this person then obviously the casino must serve him like serving visitors in general because he came with his own money and gambled without disturbing the excitement of others.
Yes, since he isn't causing trouble inside the environment, they allowed him to remain and to become a regular customer. However, if he is really mentally disabled, I think it's not right to let him walk around like that without any accompaniment by health agents or family members, because it can lead to incidents at some point and further physical prejudice to his image. Even though he is a peaceful man, maybe he is gambling with money he can't afford to lose, but due to his disability, he isn't totally aware about it and can't judge the situation properly.
So, he needs further assistance from a tutor, for an example, who could take care his money and use it to pay for basic expenses the man is currently neglecting, especially regards his physical appearance. This money should be used to take him to the barber shop, to buy new and clean clothes for him to wear, to pay for healthy food and so on.
Aside that he is not causing any trouble, I think such a player is not meant to hit problem gambling. Looking at the description, he could be mentally unstable, and if he turns out to be addicted to the game his mental problem would skyrocket because addiction also causes mental disorder. However, he gambles in a place where people don't mind how he looks provided he pays his bills, no problem. Yet such a person needs help and should be attended to as you mentioned. Nothing is wrong in accepting him into the place he is human and should be respected.
But, in a case where he is causing trouble to himself, that's not fair. Not saying the gaming house should look into his wellbeing or whether he is a compulsive player, but his family, I believe he belongs to one, should help him on that. On another flip, the player could be living a boring life due to his appearance, few people would love to associate with him, hence gambling could be his way of entertaining himself. Thinking of him, staying around people is his best choice. Regardless, many would look down on him, but someday same person will win big, provided he is not compulsive.