There are vanishingly few cases, I think, where two independent science fiction franchises could legitimately "fit" in the same universe without the need for fudging details or resorting to alternate realities. After all, SF universes tend to make their own assumptions about how the laws of physics work (e.g. how FTL travel works, whether FTL communication is possible, etc.), how the geography of the galaxy is laid out (e.g. the same star system may host different aliens in two different universes), how history unfolded from the present to the series's future, etc. So they can rarely fit together. For instance, back when the Alien Nation TV series was on, I sometimes wished it could be set in Star Trek's past because it covered such similar themes and social commentary, but there was no way to reconcile the presence of aliens on Earth in the early 1990s with the Eugenics Wars, first contact, and the like. And there were some fans who wanted Dark Matter and Killjoys to cross over, and though it seemed clear to me that Killjoys was set much, much further in the future, I was willing to buy that they were in the same universe... until Killjoys revealed that FTL communication was a novelty in their era even though it was routine in DM. (Although I suppose it's possible that the knowledge could've been lost in some civilizational collapse and rediscovered millennia later.)
