Yeah, but there could be a new parenthetical, "likelihood of an alien living in another universe, multiplied by all the effects of Fermi's Paradox itself, and multiplied by the likelihood of that alien's ability to traverse universes."
I think that would be a very small extra factor, especially if you also add the likelihood of that alien's interest in traveling to specifically this part of this universe.
And of course, we have no reasonable basis for estimating any of those numbers. We have a sample size of one universe and we don't even know the rate of occurrence of life in that one. Still, it can be fun to speculate.
