The rules state that tracings or images from the Gears of War Materials are allowable. The Gears of War Materials are only those items included in the asset pack, which are screenshots and a PSD file of the main characters + background. You can use these but I think unfortunately any artwork with other characters not in the pack are not allowed unless you drew them yourself
The Gears of War logo or text is also unallowable (though the Rift Omen is considered artwork and not a logo for the purposes of this contest.)
My interpretation of the rules was, after reading the ADVANCED set of legal speak (after clicking the submit artwork button) was that anything officially "Gears of War" was usable. I.E. Anything produced by MS and Epic Games for the Gears of War series, including concept art, screen shots, etc.
That's the gist of what I got out of the 'legal speak'. No Gears Omen (outside of the rift one they gave us) and at least one character FROM that asset pack used.. But from how I read it, I was not under the impression it had to be a character verbatim from that pack. Merely one OF him period.. Hand drawn or from other Epic content etc.