What sources? You have none. Marvel Database just placed AA in Ulti. Spider-Man universe based on pure assumption, though rightful, its still assumption. And if I were to guess, they made the assumption based on the voice actors.
Regular Guy, *sigh* I was the one who place AA in the USM universe on Marvel Database. Now this was long before the creators said they may likely not share the same world. I'm sorry for being the one who caused all this confussion.
Now could please not get into a fight over a little mistake.
AND... looks like Revan's Exile (darn! jk). Loeb and his henchmen confirmed at SDCC that Ultimate Spider-Man and Avengers Assemble WILL have a crossover event. Meaning that they're indeed in the same universe.
Well, I have no words. Not only are we backed up here, but now we have to deal with Ultimate Spider-Man content too?