I would say yes, modders are artists. Some are fine artists that work with visual aspects of the game, others are performance artists that work with game play. Are all of them good artists? Well, that's open to personal opinion. I studied art history in college and think some historical pieces are horrible. Some are, literally, gross. And I don't like them - to me, they are bad art. But they are still art. Modders that tweak existing content, making it better, worse or just different are also artists. After all, one of the best known pieces of art was a signed, mass produced urinal.
