You don't find this even the least bit confusing?
The rabbi is in Tehran during the Holocaust deniers' meeting shaking hands with someone who calls for his death...
Uh, no. He's shaking hands with someone who has the same view as he himself has as regards the polity of Israel. They may or may not share views on the Holocaust - it's not entirely clear to me what Ahmadinejad's views on the Holocaust are, exactly, except for the argument that it cannot be used to legitimate the existence of Israel. Nor do I know what this rabbi's views on that issue are.
Of course Ahmadinejad invited Jews to his silly conference, as an exotic touch of colour [and to highlight to the West (what everybody *should* be aware of anyways), that exterminating world jewry is not part of Israel's foes' agenda.]
Duke's probably there for the same reason - to an Iranian audience who's not aware of Duke's record, he's just an American politician who's at their side.