Are you talking to a land base casino? if yes I would say no, they are not criminals since the casino needs permission from a goverment to run in a city and they not conmen too because players will not enter and gamble in their casino if it is true.
Yes exactly, I don't know why OP is having that question. It is pretty obvious that a big casino couldn't just keep running if it was illegal or was ran illegally by criminals. All the casinos require a permit by government, and if you see any casino running it means it's permitted by the government after doing all its checks.
It's completely other matter that criminals do gamble in these casinos but that's nothing the owner can do about.