I think it's not just about control but more about how someone can understand it and also maintain awareness of the dangers of the risks that lurk, because that way I believe that it is unlikely for them to lose control or get caught up and carried away by the situation.
Yes, I grabbed a whole lot of sense from what you just said, and it's true what this individual may be lacking is self-control, because for the fact that the person O.P is referring to became addicted to gambling due to the fact that he was working in a casino, is a clear sign that that's the same way he would have continued gambling if he wasn't working in a casino. Because thou the environment a person finds himself may have influenced on a man, so for me, I think this guy was already into gambling before they got a casino good.
some time we may not understand better and try to throw blames at people for their habits and think its because they dont have self control only for us to later see that even us if in same shoes may sometimes not do any better rather we may suffer same fate, self control and discipline are two attributes that are not easy to posses at most point especially when we have to put in conscious efforts to get such done.
some gamblers are actually disciplined but may have a driving force which arose from certain stuffs and they will start to behave in patterns that feels like they are not disciplined enough or lacks self control. gambling some times with certain needs in mind could be the problem some of these gamblers have got basically.