He was clearly a Best Actor nominee. The movie had two male leads, Hurt & Brooks. I mean they give Anthony Hopkins a Best Actor nomination(which he won) for Silence Of The Lambs but give Brooks a Best Supporting Actor nomination. I'll never get the oscars.
It's a classic case of marketing/campaigning. Hurt was the better known actor at the time (having just won for Kiss of the Spider Woman), and they figured if 2 actors in the same movie are nominated in the same category that the vote will be split and neither will win. This way, Brooks has a chance of winning as Supporting.
Pulp Fiction did this also with Travolta and Sam Jackson. Ironically, none of them won!
Even a broken clock is right twice a day