The Character that attempts the action is the one that is game checks. Not the leader.
Should the leadership states that if is unresistable (like JTR expose) the whole check is overridden.
In any case, it first has to land (evasion check) and again is made with character attempting the action.
In fact, what happens is that the leader ability is copied to each character kit that it applies to at the start of encounter (be it an ally or an enemy) and stays there until the end of encounter. Even if leader is defeated, ability stays.