Yes, it may be considered legal.

Nullum crimen nulla poena sine lege- This means that there is no crime if there is no law punishing it. This is a legal principle which is accepted in most countries that state that a person is not criminally liable for a crime that the law does not prohibit.

By applying this principle, if there is no law expressly prohibiting an act, then it is not a "crime" under the eyes of the law. Again, if there is no law punishing a person from gambling activities, then it may be considered as legal in all its precepts. But to be sure, you have the obligation to show that there exists no law that expressly prohibits gambling.