Oh, that's cool, but i think if you're comissioned by the official company, then it's no longer fan art, but commisioned work? Like for example Artgerm does some illustration covers for DC comics, but that's not "art made by fan as a hobby", and more the company paid that artist for the art.
"Fan art or fanart is artwork created by fans of a work of fiction and derived from a series character or other aspect of that work. As fan labor, fan art refers to artworks that are neither created nor (normally) commissioned or endorsed by the creators of the work from which the fan art derives."
source: https://en.wikipedia.org/wiki/Fan_art
Well in that link, they also cover a little about copyright laws about fan art.