This is also a break in the trust relationship between the casino and the gamblers, if they are doing that. It takes only one honest whistleblower to expose practices like this... or a skilled white hat hacker to show other gamblers what they are doing. 
I think they can use this same argument to answer your question. Since doing something like this can damage their reputation and potentially make them lose customers, there is no need for them to cheat their customers. Plus it is easy and probably hard to prevent since anyone can be a white hat hacker even though they seem so greedy. Not to mention the cost to cover any giveaway is probably not that big compared to all of their expense.Obviously, they can simply lie and the owner can simply lock out any access to sensitive data for his workers. Not the best answer to hear, but probably the one that will likely be given if you ask them directly. Snce they probably won't give any data about this, if you're suspicious about something like this, the only thing that you can do is probably do the data digging yourself or hire a white hat hacker to do so.
