Great question, OP.
Is it possible to work in a bar and not drink alcohol?
Is it possible to work in a cigarette factory and not smoke?
The answer is always yes and many people manage to do that.
If your friend has a problem staying away from gambling and his casino work is leading him astray, he should find another job.
when they work in a field of course it does not mean they do the same thing. because I think there are some people who work of course it is a demand of their needs. for example those who do not smoke but because of their needs that must be met and there is only work in a cigarette factory, most likely they will take this job but smoking or not is a decision from themselves, if they do have a strong reason not to smoke then it is not strange if they are not smokers even though they work in a cigarette factory.
besides that we all have our own choices in determining everything, so even though we work in a casino it does not mean we like to gamble. also if compared to guessing it is difficult to determine which is more of these two things, whether they work in a casino and at the same time gamble or those who work in a casino but purely do not gamble at all.
I myself think there is a possibility that people who do not gamble even though they work in a casino, maybe even a lot.