Actually, fanon just refers to a headcanon that's commonly accepted by most authors within that fandom. For instance, one popular fanon is that the Krana-infected Tahu faced either Gali or Kopaka the same way Lewa is confronted by Onua. Fan fiction is just that, fan fiction.
If something was made as fan content and became canon, it's just plain canon. Anything confirmed by Greg, any of the Dark Hunter models, Krakua, etc. are canon.