You know, it could be. But I'd have to look at Mike Holmgren first and foremost. And I remember an interview where Holmgren stated that Walsh taught him pretty much everything that he knows, so...
Walsh 49ers: Montana, Young, Bono, etc.
Holmgren Packers: Favre, Brunell, Warner, Brooks, Hasselback
Those guys just know their s*** when it comes to quarterbacks.
And being around Favre certainly helps, although I'm not sure how much it did for guys like Ty Detmer, Doug Pederson, Henry Burris, etc.