It has been noted on occasion, usually by Vorta, that the Jem'Hadar are in fact difficult to control despite their genetic loyalty to the Founders. It makes sense to me - the Jems aren't like Star Wars droids or even clones, who just slog across the battlefields as proxy soldiers. They're clearly highly individual beings with strong drives and desires that they relate to with a fully conscious self-awareness. They're designed to be more than what they actually are, I think. Yes, they may be disposable, expendable fighters but really they're not truly cannon fodder - they're engineered warriors in the fullest sense. They're bred to be intelligent, aggressive and driven to succeed, and it's implied if not stated that they feel contempt for anything that isn't a Founder (presumably a programmed trait to aid their bloodlust). I imagine it's simply not possible to give them these traits and not have them operate as individual, fully sapient beings with a self-concept that can question itself, and adapt if desired. Perhaps it's "fortunate" that Jem'Hadar die young, before they've accumulated enough experience to start really questioning. Maybe it's only this that prevents widespread rebellion. I suppose it's a case of the Founders doing their job a bit too well. The Jem'Hadar are designed to be the perfect soldiers - but how do you balance the need for that soldier to be loyal with the need for them to demonstrate sophisticated reasoning? The Dominion probably is balanced procariously on the compromise. I always imagined it's not nearly as stable as the Founders would have the galaxy believe.