I have an AVIC-Z150BH in my 2005 that Crutchfield said wouldn't fit. I had a P3400 in it before that Crutchfield said wouldn't fit.
I suspect their concerns centered more around the depth of the head units. Both units fit, but they're tight in the back. It's a concern more for the wiring than anything else.
I hacked out a section of the dash support - in front of the OnStar receiver - to give more room for the wiring. If access behind the dash were better, I might have been able to route the wires without doing that.
Remember that you've gotta make room for two adapter boxes, one for the amp/BCM interface and the other for the steering wheel controls. It's there, just make time to do it.