I'm not sure about the blinkers, but I wanted to have clearance lights on my CC, and when I looked for the wires under the headliner, there was no provision for the clearance lights.
I think GM makes every wiring harness specific to the VIN and the options ordered to save on $$. If you do not have turn signals in your mirrors now, you probably do not have the wires to make a new mirror light up.
That is not a real big deal, but you will have to run some wires yourself to connect the mirror turn signals.