do you think it's right that he transfer you to another department that has nothing to do with money?
Actually transferring an employee that has a gambling disorder to another Dep't is a generous act of the employer because he keeps him away from losing his job if ever the gambling disorder kicks in, at least he is blocked from the temptation of using the company funds for gambling.
Provided that his salary is the same as when he is in his old department, and it is very similar or very much within his skill range, it's not on demotion or promotion, it's more on protecting him from the temptation of committing something because of his addiction and besides the manager or the owner has the prerogative to do what he wishes to do based on what he thinks s right for the good of the company or organization.
But if he can't overcome his addiction, it's likely to be difficult for him even if he can earn the same salary as his old department. This may be about overcoming the problems that he had in the past and it seems he really needs help from other people who can provide support for him to get out of his problems. The company can only help as needed while the rest is up to him because the company can't do much for him.
Companies usually require their employees to follow a certain standard that are fit to the company. They must abide and adhere to the company policy as well as the proper decorum as their position carries with them the responsibility of the company name.
If an employee has a gambling addiction and his performance is being hampered by such, then I think the company has every right to protect their employees into such when it hampers only their performance. But if the employee can still produce quality work despite having such addition, I think the company will not address such issue.