This is a feature used in Ludum Dare, where jam game submitters can opt-out of categories where they have used pre-made assets (e.g. opt-out of the Music category if they use pre-made music). This makes the final rankings much clearer and more meaningful to the other entrants (e.g. who created their own music during the jam).

Yes. Is pretty much needed. I'm in need of this too and several people have brought the ludum dare's voting system as one of the best. This sholud be included.