If they create fanart (art based on already existing anime/manga series), they could I suppose be approved here under Fan Artists, but the fanlisting approved here would only cover them in regards to their fanart creations, not the rest of their artwork (and from my quick look around their sites, I don't think they're predominately fan artists). I'd suggest sending a contact form to the Arts staffer at TFL to give them additional information and to further discuss the issue. If they're published digital artists, I'd imagine they would best be approved in the Art category at TFL somewhere, but I'm not sure if they approve digital artists. They don't really belong here at TAFL (especially since they seem to be published artists - I wouldn't consider them fan artists and they don't have anything to do with Anime or Manga really).