I had an aftermarket remote starter installed in my 2007 Cobalt at a shop and they had to put in a bypass to work with the GM Passkey. I believe it is necessary in order to start the car because of the Passkey system in the car.
With all the wires, if connected properly it will do things like check to ensure the car is not moving, the e-brake is set, car is not in gear, etc. If it's not done correctly you could cause damage to the car by trying to use the starter.
I personally wouldn't risk it unless the car was well out of warranty. I had mine installed at an audio/alarm shop with only a few months left on my factory warranty, and the dealer said any problems involving any parts that were modified during the installation of the remote starter would not be covered after it was installed.