I believe some other users here might have answered this same thing, but just incase, you need to know that this is something you can possibly only find out from casinos alone, or possibly someone who have worked in a casino before, if such a person is a user on this forum, then expect an answer if he or she will be willing to share.

But aside from the above, I will like to let you know that there are softwares that can accurately, or close to accuracy; detect and tell if a user is accessing a service or site through a VPN, and this mostly work if the user is using a free VPN which usually comes wit a shared ip address.
Maybe by searching through google, you may likely find some of this softwares, but it's hard to tell which works and which doesn't until you try them.