To be honest, most schutzhund trainers will not take on any other breeds besides the ones most well known in the sport (ie. germans shepherds, malinois, dobermans, rotties, bouvier, giant schnauzer, and mixes of the above) and a lot of times german shepherds are the preference. They like to ustilize the large, high drive, working breeds. I myself, have never heard of an auzie in the sport, however, it would be interesting to see some less well known breeds compete in the events.
A tonne of training is involved in the sport of schutzhund, and no, unless improperly trained, and or not finished, schutzhund will not make your dog aggressive.
However, schutzhund does not just consist of bite work. Tracking and obedience are all part of the venue. There is a lot more involved, and obedience is the number one factor in this sport to succeed. You can have a dog with a perfect full bite, with no movement and no shyness, who is a whiz at the "attack" portion, but if you don't have a solid foundation of obedience you don't have control over the dog who you need to eventually "out" from its target. Obedience is the key even to the protection phase of the sport.
I would contact a couple local clubs and see what their polocies are on training, what breeds that they take, and what their particular training involves. I would also suggested going to watch some trials to get a feel for what really is involved and how others handle their dogs. Most schutzhund dogs are conditioned right from puppyhood, building upon the drives as young as 8 weeks.
I know that Auzies excell in agility, disc, obedience and herding, and it might just be better to stick to those venues. You really need to research the sport, go to trials, speak with trainers and trialers alike amd really find out whats involved. Once you get to the bite work portion, you really don't want to stop mid-way through training without being fully able to control this drive. It takes a lot of work to excell at this sport.
Hope this helps a bit. Good luck!