In Our Town in Act II, who is the "real hero" of the scene that the Stage Manager talks about?"The real hero of this scnene isn't on the stage at...

In Our Town, you're right in thinking that this is a vague reference to "the real hero," for it is. The "real hero of this scene" isn't defined but hints, clues, are given to the identity of this "hero." First, the line is spoken by the Stage Manger who is playing the minister for the moment. By the way, the players don't know the minister is really the Stage Manager, only the audience (or readers) knows that.

The second clue is that the minister speaks of nature attempting to make a perfect human being. In Christian theology--and Christian theology is relevant to the scene because it takes place in a Christian church--the perfect person in Jesus, who is part of the tripart Godhead.

The third clue is that the minister says "quality" is why he is in the ministry, which is a Biblical allusion connected to Jesus as the one, in Christian theology, whose writings teach how to attain a life of quality. The final clue is an indirect one. It is before God that Christian wedding vows are exchanged. Therefore, after putting these vague clues together, the only conclusion is that "the real hero" is really God who is the author of marriage--as in the Christian creation story--and the One who will sanctify the upcoming marriage.