Ok. Been tossing this one back and forth for a while now on this forum. Thought it a) belonged in rules section and b) deserved it's own topic.
That said, while playing with battlescribe it only allows you to select this strategem once. (by no means do I think that is definitive).
But that got me re-reading it again.
I can still see the argument either way, but here would be what I would point to if I were trying to argue that you can only use it ONCE with RAW. (Since this will be the most likely argument we would have to counter if we tried to use more than once).
Alliance of Agony states ".... Choose UP TO one Haemonculus and UP TO one Succubus...." [emphasis mine]
by contrast, Screaming Jets tells us to ".... You can set up a Drukhari Vehicle......"
So the difference being the up to.
The argument would be that no matter how many times you played the strategem, you are still limited to the up to one. This argument is predicated on the fact that if you were able to use this multiple times, the "up to" wording would be redundant.
Of course the counter to this would be that it is up to one for each time you play the strategem, and the "up to" is necessary to make it clear that you can just have One Haemonculus gain the benefit of the strategem and no Succubus (or vice versa) such that you don't need to have both in your army.
I suspect RAI would be the former case, but wanted to start an official discussion to flesh out the argument here.