This is a really interesting question; a few thoughts come to mind ...
Yes, things can interact. A large chunk of Ted Lingles Coffee Cuppers handbook explores the interaction of basic tastes in coffee; eg. how sweetness and acidity interact. You can get a sense of these interactions by tasting solutions of varying concentrations of salt, citric acid and sugar and mixing them. I suppose that different types of tastes will interact with each other as well; for example, rather than simply adding up, blending two coffees with different types of acidity might lead to that elusive and wonderful "juicy" quality. The extent of these interactions is something that would be interesting to explore.
Next, there is a very interesting idea that blends might perform worse when they require a grind setting that is different from the optimum grind settings for each of their components. To try to explain that more clearly, imagine that you have a blend of coffee A and coffee B and you would grind coffee A at grind setting 7 when extracting it as a single origin and you would grind coffee B at grind setting 9 as a single origin. The blend might grind at grind setting 8. The idea is that one of the coffees will be underextracted to some extent and the other would be overextracted. I remember that CS member Reuben did an experiment on this a while back. An interesting experiment might be to determine the grind setting for the blend, then extract each of the single origins at that grind setting and see what they taste like.
All of this points to the value of a roasters skill in blending.