Marketing or education would be how I put it in my taxes. (my accountant knows better than me).
If you are concerned with the legality of it, you might want to considerate incorporating your business (you might want to do this if you are making enough from it anyways).
I don’t think we have anything to worry about after talking to lawyers and accountants, but if you have concerns talk to a lawyer in your area.
I had my lawyer look up any gambling court cases over the last ten years, and feel comfortable being an affiliate.