I don't think it will illegal.
It depends where country you live, because some countries banned the use of bitcoin. In some countries they allowed the use of bitcoin but they don't allow gambling.
Bitcoin is not banned but most countries are trying to regulate them to put taxes and make sure they are not using for some illegal activities.
Bitcoin ban is nothing to do with gambling. Online gambling is banned in most of the countries including in my country but still, people play with bitcoins.