i'm pretty sure there are. but i don't really use different people from my party every time i leave camp i generally just use the same 3 members so there are lot of dialog that i haven't heard. that's one of the things i love about the game lol. i think there was one involving alistair, morrigan, and wynne but i can't remember.
Currently Playing: Assassin's Creed II, Grand Theft Auto: Episodes from Liberty City, Mass Effect 2
They're uncommon, but there are a few. I suggest getting one of the mods out there that increases the number of points NPCs talk to one another. There's a surprising amount of dialogue just two characters can have which could potentially not be heard in the base game even if you kept them in your party as much as possible.