I think that the presence of such employees depends on the size and profitability of the casino. The larger the casino, the more serious and professional its security service is. I think the biggest casinos in Las Vegas and that's where the best security services in the world are.
For me, as a player, the main thing is that I can enjoy the game and no one interfered with it.
The bigger casino doesn't want to see their reputations damaged because of the small mistake, so they make sure that they can handle their environment. Maybe they are placing their employees as gamblers, making sure that everything can run properly and make money from their place. A gambler who only want to enjoy the game and having fun in the gambling will not want to think anything. They will let the casino handle everything.