What's the use of having employees pretend as gamblers? If they were found out, it could easily be seen as a way to manipulate the mindset of the customers that gamble. An easy example would be the employee pretending pushing the others to play with him and the like. Just let them be a normal employee, there are cams all over the place after all so any suspicious activity could easily be seen, as long as no blindspots are made that is.
Phew, I am sure the employees can hiding their identity among the other gamblers. Or another scenario is the casino can hire some pro gamblers who will watch the games, and report it to the security so the cheater can get arrested. There are so many ways that the casino can do to protect their business from people who want to cheat, and maybe that is only one of many ways that they have.
Two-and-a-half years ago, in one of Japanese casinos I have the good fortune to be experiencing the communication with employed robots that acted as professional schillers in the spot. And from what I observed, their second duty was watching the games, but to what purpose I don't know.