by BTBAM
The surge rules don't talk about ambush, but the ambush rules talk about surges. They say surge minions (granted it says from the card, which I assume goes for special surges) do not ambush.Edit: posted above me
As for when the room is clear, do they ignore ambush, they wouldn't have to. At that poit you'd reestablish initiative order.
I don't see much sense in having the boss cards back to back either, I just didn't recall an ambush being something I encountered with boss minions.