I'm pretty sure all leaders end up on the challenger board for some reason. Plus this will be fun, I hear a challenger must defeat all 3 with 1 team. If they win against leader 1, and lose to leader 2, they're allowed to change 1 pokemon, but if they choose too do so, they'll have to re-battle any leader in the triad they've beaten. Badges are given after you've obtained all 3 wins.