Late in the game "Assassins Creed IV: Blag Flag" woman comes to you when you're out of the Animus frantically telling you that the head of Abstergo Industries, Olivier Garneau had a meeting in Chicago ("Watch_Dogs" takes place in this city) but hasn't returned. In one mission in "Watch_Dogs" you have to kill Olivier Garneau which puts these franchises in the same universe (no surprise since they are both made by UBISOFT).