My experience has been that they are not. But that could be some insert issues as well.
Currently I use hot melt. So I can heat up the head and twist it to where I want to be. It works, but is not perfect.
It wouldn't surprise me if the higher end machined broadheads are. Valkyrie, cutthroat, vpa etc.
But for normal components you've got two sets of threads to worry about. Insert and broadhead. Obviosuly both would need to have the thread machined the same from part to part.
It really wouldn't be hard. Just implement your machining processes such that you start at the same spot every time. I would think cutthroats and vpas likely have similar threads from head to head.
But there could be a market for inserts that have identical threads from part to part. hint hint, wink wink...
That way any broadhead that's indexed could screw in to any insert that's indexed and every broadhead would align the same and any arrow.