As far as I know, every member's opinion counts. For example some member may have played with a certain applicant before, and therefore can provide a more objective/detailed opinion. He/she can also post replays which prove the level of skill of the applicant. Or if the leaders say yes to a dude and a member has proof that said dude is a douche, he/she can post that and influence the leaders' opinions that way.
But if at least one of the leaders gives a definite no to someone, he won't be accepted unless that leader changes his/her opinion. Even if the other leader gives a yes, it won't make a difference in that case. That is to avoid conflict in the clan, since there is little point if one leader favors a dude and the other leader has an intense dislike for him. At least that is the way it has been for as long as I can remember, and I've been here a long time.