Did you know there was a Fallout 1, 2, Tactics and Fallout 3 vanilla game?
All of which depicts aliens as Easter Eggs/non-canon elements and that the game is about humanity and not aliens? MZ contradicts the entire series including Bethesda's vanilla game and most Fallout following forum members have been against aliens in Fallout. I very much doubt that a poorly received DLC would overturn the entirety of the series (and yes, it was poorly received as evidenced by both fan and critic ratings).
On that note, this thread is about TES in Fallout. My mentioning of aliens was merely an introduction to my post as a way of comparing the issues.
Edit: If you do want to argue aliens as canonical elements in Fallout, there are dozens of threads floating around about aliens. I would just prefer not to derail the thread.