The GMT900s already have a CAI system.
Yes and no. The airbox does indeed feed into a sealed opening in the fender, so yes it draws cooler air. The stock airbox and panel style filter flow very well. That doesn't mean there isn't room for improvement in the system, though. Ditching the OEM intake tube that goes from the MAF sensor to the throttle body will net some decent improvements because you eliminate all the excess baffling GM adds to quiet it down. This is why the Airaid Jr kits are so popular - everything you need, nothing you don't.
The tradeoff is that your intake will be louder, and some of us have had issues with fitment and vacuum leaks while using the Airaid jr kits.