Following the answers by TheLethalCarrot and RubenDefour, it is highly possible that the Watchers are not capable of the fourth-wall break.
The only connection I could find is here. This page dedicated to Uatu provides the list of all his appearances throughout the Marvel stories and mentions that he has been aware of the fourth wall and talks to the reader quite often, one of which is the following:
The five-page mini issue titled Tales of the Watcher: The Saga of the Sneepers, released with the mainstream Tales of Suspense Issue #49, the Watcher Uatu introduces an alien race called "Sneepers" who are monitoring the Earth since the time of cavemen.

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Although this does not say much if Uatu is talking to us readers, some points indicate that he mostly is. Firstly, he does not mention the presence of any superheroes in his story (which is the case of our Earth). Secondly, the events such as Cuban missile crisis, Vietnam crisis and the Soviet Czar bomb.
In another instance, five-page mini issue titled Tales of the Watcher: The Primitive, Uatu seemingly addresses the readers as mortals (funny, this immortal prick is!) and reads us the story of two brothers Paul and Vince Harding (image below). The final page from the issue shows Uatu closing the book and walking away.

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These two instances are mostly likely the indication that Uatu is capable of breaking the fourth wall.