I wonder would Vipers form polycules with each other?
Probably!
The Elders seem to have a Thing about letting their subjects have too much freedom to procreate - you have the Sectoids who are all cloned from the same base, the Vipers are only allowed one singular male to bring in the next generation... It's easy to extrapolate from that, that our human norm of monogamy and marriage is outright discouraged among the Elders' subjects. You don't want your cannon fodder devoting to each other or to their children more than to their gods.
As such, Vipers (and likely, other aliens) probably are more likely to form polycules, or at least are more likely to have their own hook-up culture which is far more normal and less stigmatized than it can be among humans. Granted, the Elders probably don't like it that much better, but banning sex/romance entirely would be impossible. Better that (to the Elders' minds, at least) their subjects consider each other replaceable just as the Elders do.
I can imagine it as a site of culture clash after the occupation was over and aliens had to integrate into human society rather than exist on top of it.