I'm not sure what the percentages are between "Comic-aware" and "Comic-oblivious" movie-goers, but I would think that even if the "Comic-oblivious" group didn't get it... they would in turn be intrigued and maybe ask questions of their "Comic-aware" friends, or just scratch their heads and move on. Maybe it compells them to see the Hulk movie possibly to find out... even if that movie does not follow up with it. I'll agree that the cameo woud have to be inserted in such a way that does not confuse the story for those indivduals, but I can't see it being a negative if some don't understand. Even though some of the writing on the Simpsons is geared towards the adults... it does not seem to hinder my kids enjoyment of it and there may be even be more material percentage wise that they don't get. You see "inside jokes" or "in-the-know-references" not intended for the majority viewer, in other films like Shrek and other Disney flicks for instance.
I recognize it would take effort to coordinate the cameo appearnces but I still feel it would be a mutually beneficial strategy for all the studios to unite the Marvel Movie Universe, even in a small way. I don't recall if ever there was a series of movies linked with one another quite like this.
In a way it's like Norman Lear's TV series'... many linked with one another in a big TV Universe... All in the Family, The Jeffersons, Maude, Good Times, Florence with TV crossovers.