Whoops, I'll fix that! Meant it to be blue.
Done. I'm going with only IN, because IN crews are "corruptible", as it were, being mainly indentured crews and whatnot.
Space Marines know the Tyranid threat, and would never surrender a vessel or work alongside, unless it was like an Inquisition shadow corvette or something, which isn't represented by the rules yet anyway. So, no SM. Same would go for AM.
Still, just having any other artificial vessels would be quite beneficial to Tyranids. The ability to take a cruiser, or even escorts of any of the allowed fleets could change tactics quite a bit.
For that matter, I'm still not totally sure on the AM fleet. I'm thinking they may be more willing to ally to the Tau to acquire technology or something, but then that's not their thing. They're so insular and looking for human tech, so I don't know. Opinions! About any of it, for that matter.