I don't think you need a unanimous vote to be boss or win a commission ruling for that matter.

However, I'm pretty sure the captains could see the writing on the wall. Even if Jimmy Brown, Marino, Gaggi, Joe Butch or others felt that strongly about it, there was something like 22 captains at that point so it is possible that they would not be in the majority. Better to wait it out and let the Commission deal with it rather than formally oppose your boss and start a war.