You need license anyway. Nobody will trust you without it
he can run a casino without license but no credibility. just look at the gambling section. there are several casinos, dice sites or betting platforms that have no license yet. not even the curacao gaming license. and yet they are operating. only those gamblers that want to risk will play on that site. or they will try playing, but they will deposit small amount of money. and that is understandable for a substandard casino.
so i dont think the OP can attract traffic before acquiring his license. that only shows that he has no sufficient funds to hold this kind of business.
Basically one can start operating a casino without a license, but since we are engage into business and we also look its long term success, it's better to registered it already so you won't have any changes in the future. Remember that you are carrying a name, and that name will be the face of your business, once that is ruined due to legality issues, you can easily loss your customers which you have been building for years.