I've never seen any studies on pellet vs. whole aroma, but I know Vinnie at Russian River uses pellets, and he's a freak about anything that affects hop aroma. He won't distribute Pliny bottles within a few states from California because he so worried about hop freshness, even with the whole country begging him for it. I figure if a guy like that knew that he could get more aroma out of whole hops, he would be using them.
I tend to use whole hops in the boil, and pellets for dry. It just works out that way for me and my system, I order all my kettle hops in one bulk shipment in the fall from Freshops. I can't swear that I would get less late addition aroma from pellets, but my boil kettle system doesn't like too many pellets, so I can't comment on late hops. I certainly have not noticed any difference in dry hopping, as I have used both. In fact, the pellets seemed to be more assertive. I do know that when I've used bittering additions, oz. for oz. they seemed more bitter than whole.