It could go both ways.
On one hand, it's important for a young coach to have veterans he can rely on, and who know how to play winning, team basketball. A coach's message can get lost if the veterans tune him out, and one way to make that message resonate is to have team leaders who buy it.
However, Rondo isn't necessarily known as a guy who buys in. He's been known to give his coaches a hard time at every level he's played. He reportedly was a vocal dissenter in the locker room, allegedly leading a mini-mutiny by the younger players a couple of seasons ago.
My guess is that the Celtics brought Stevens on board to be a teacher as the team rebuilds with a youth movement. I'm not sure that Rondo will be consistent with that, but I'm not around the team on a day-to-day basis. Danny seems like a believer in Rondo, and if he ultimately decides that Stevens can coach without being steamrolled by his hotheaded point guard with the extraordinary IQ, then I guess we all have to trust him.