Dungy was the nice guy of all nice guys. Players said Dungy's version of chewing the team out was saying "Gentlemen, we can do better then this."
I don't think being nice necessarily means one is a bad coach.
Also as someone pointed out, you don't know what goes on behind closed doors. These are just clips of Reich that the Colts made public. If he started yelling at a player and getting in his face, they probably wouldn't put that in there anyways. And I also don't think that you necessarily have to yell at players and get in their face.