There are two protocols that are used in the VE.
The first one is the GM Fast can protocol, which is a two wire system (Which I know very little about), used by the critical vehicle stuff such as engine (ECM) transmission (TCM), ABS and Stability systems.
The other is the GM Single wire 29Bit Slow Can protocol, which is used by the the "comfort" devices and non vehicle critical stuff.
(Such as HVAC, Entertainment, Instrument Cluster, BCM door, lights, park assist, Sat-Nav, etc, etc...
This I do know something about, and have been messing with this for around 1 month now, an have worked out a number of things.
(Such as parroting the park assist data to display park assist information on the colour LCD screen), door status information such as lock, unlock, boot release, drivers, passenger and back door open / close status, sending and receiving steering wheel button commands, some radio button commands, and kinda almost getting the RGB input for the sat nav working. (We can send a sat nav command to mute the radio for audio injection)....
There are lots and lots of things to learn and play around with in terms of the GM 29Bit Lan, so I think people will be playing around for years to come...
Here is some information on what I have, (and many others) have found so far.....
www.carmodder.com • GM Lan Single Wire CAN Bus Sniffing
Hope this helps