Soldier, Blade Runner and Alien are the same universe. This is Word of God from an interview with Ridley Scott. Todd’s generation of soldiers were predecessors to their genetically-engineered replacements. Their replacements were the predecessors to Replicants, who were predecessors to the synthetics from Alien. Weyland was a protege of Tyrell.
At the beginning of Soldier, we see Todd’s service record, which includes references to the same events Khan Singh mentions in Wrath of Khan. Given Todd’s timeframe, he likely fought against Khan and his fellow Augments in the Eugenics Wars.
Therefore Star Trek is the same universe as Alien.
Since the stardrives in Alien are so slow, we know the Xenos inhabit space (in FTL travel ranges) pretty close to Earth. There is no way Starfleet was letting a threat force like them hang out anywhere near major worlds like Earth or Vulcan. We see no Xenos anywhere in Star Trek. They dig in like Alabama ticks any time they get a chance, so we can determine they’re either extinct or damn close in the area encompassed by Star Trek. Combine this with their obvious priority as a threat force, and there is only one conclusion: Starfleet (possibly acting with allies) engaged in a quarantine and xenocide campaign against them.
Two other points should be added here.
Judge Dredd is high tech, but not even close to what Starfleet is throwing around. When Dredd and Sanchez were impregnated by facehuggers, the doctors at HQ managed to remove both of their aliens without killing the Judges or aliens. Learning how to do this resulted in the death of one impregnated Judge and at least one doctor, but they figured it out pretty quickly; we don’t see any other attempts, and they operate on Dredd and Sanchez within a few days of their first attempt. Unless Starfleet was run by abject incompetents (which may be possible, considering Enterprise and Voyager), that information is either in their medical database or reproducible by their own doctors.
Fun addendum: Alien and Predator are also a shared universe. Predator 2 and the Aliens vs. Predator series make this impossible to argue against. Yautja (Predators) are green(ish), and they have two sexes. Captain James Tiberius Kirk has at the very least fantasized about nailing a Yautja. He is unlikely to have succeeded or even made a serious attempt, however, since the Predator books establish their women are far more dangerous than their men and Kirk is neither dead nor maimed.
And for the humorless clods: yes, I realize this isn’t actually canon. Lighten up. It’s Star Trek, not the Meaning Of Life. And if Star Trek IS the only thing giving your life meaning, you really need to get out more.