And it's been pretty well established that the Super Mutants can't be talked to. Which makes them the new Orcs, a point I'd made months ago, and which is still pretty upsetting.
I hear there's rumors on the internets [spoiler:910a409440]about a scene involving an intelligent supermutant, which the PC talks to at some point. It's apparently as smart as FO1's Lieutenant. [/spoiler:910a409440]
So no, it's not established in an absolute sense. Sure, the ones you encounter in the game world you can't talk with, but then again you couldn't talk with the random encounter ones in FO1 either.