The internet I have come to agree that it does not have all the answers or say the section of the internet we have access to does not have all the answers. When it comes to the legality of crypto denominated gambling, I think a visit to the gambling section of the forum would provide answers and focus should only be on those sites that have been in existence for long and are big enough to have legal troubles and how they deal with it.  There is equally a thread on the economic of gambling on a country but with more pressing, he could give a report on crypto specific. I know some obtains license from some countries which gives them the legality to operate. For US and China citizens, they are restricted to participate in ICOs, the same reason why they are also not allowed to participate on crypto gambling sites.