I don't think only hardcore fans will recognize Dum Dum Duggan. He's pretty much everywhere these days, including the new Avengers cartoons, as well as appearances in high profile comic book titles (including covers) during the Civil War and Secret Invasion summer events.
Heck, even the loud guy behind me in the movie house shouted "Uy si Duggan" when he first appeared in the prison break scene.
Of course, he would reveal his true nature a few seconds later when his equally loud seat mate asked "sinong Duggan?"
His answer: "si Hacksaw Duggan," stated with absolute confidence.
What hardcore fans will recognize, I believe, are the Howling Commandos. Though their group wasn't mentioned by name (though I may be mistaken about this), 2 of the original members were perfectly represented... minus a younger Nick Fury for some strange reason.
Now, the super hardcore fans will be the only ones who will recognize - without resorting to cheat sheets - the appearance of another member of the Invaders team aside from the Human Torch (and Bucky Barnes)... the un-costumed Union Jack (first iteration) in the form of Montgomery Falsworth.
I believe everyone appreciates these "easter eggs" planted in many of the Marvel movies in the shared universe, especially when some of these easter eggs actually prove vital in latter films. DC Comics should take down notes. For all the almost 3 hour spectacle that was Green Lantern, not a slight reference to other characters nor other events was ever included.
A
the whole thor, iron man and captain america movies were based on the Ultimate Universe continuity (most notable story arc was the civil wars tie-ins).
Civil War did not happen in the Ultimate Universe. That was regular continuity. If you'd recall, by the time the Civil War was taking place in what you refer to as the 616 universe, Jeph Loeb was busy destroying the Ultimate Universe in a crapfest he called Ultimatum.
Additionally, though the movies are visually inspired by their Ultimate universe counterparts because of the latter's more modern take on these superheroes, they are not exclusively based on the Ultimate universe comic books. Iron Man, for example, used the 616 model for its origin story, swapping elements for their modern versions. In the Ultimate version, Tony Stark wasn't trying to survive from shrapnels piercing his heart, he was trying to survive from brain cancer.
