Nope. In a field one can be an amateur or a pro, but not both simultaneously. They're opposite ends of a scale (in most cases, the only points on that scale, but that's neither here nor there).

"Fan" isn't on that scale, at least not in this case. It's kind of like a question on the ICG list a few weeks ago: "Is costuming a hobby or an art to you?" The question is invalid; it assumes an exclusive relationship that doesn't exist. It can be a hobby and an art simultaneously.

Some of the confusion probably comes from fanzine, semi-prozine and prozine. Semantically, they're all really fanzines, it's just that a "fanzine" is specifically an amateur or non-commercial fanzine.