From what I understood/inferred (and it's hard to keep those two apart now) it's not clear whether Hiro ordered it, or someone ordered Hiro to do it? I think Hiro ordered it, yes. It couldn't have been Wo Fat, I thought, for the reasons you described.

But I think Joe's helping him because Hiro's a potential witness against Wo Fat. You know, "the enemy of my enemy is my friend"? Wo Fat is tying up loose ends, yes, although it remains unclear how much power Wo Fat still has (I'd say, a lot.)