Those are the only ones we know were involved. There has always been rumors that people were involved on both sides (Setting up the screwjob and warning Bret), but their identity hasn't been revealed.
I believe Meltzer has always said a key player has never been named, and he won't be named until he dies, which makes me believe he's kind of up there in age.
All of the guys in the locker room at the time, I have this feeling that Undertaker must have known SOMETHING then. Just because of the stature he had with the company, he must have either known or seen something coming.
Undertaker was pissed off at Vince for the whole thing, and even forced Vince to go talk to Bret - and we all know how that ended.