Sounds like you did all the right stuff (perhaps we need to call OnStar first as it DOES seem the dealer won't know much). Definitely have it checked! It would be a shame to accelerate up to 65 and not be able to stop!
If the ABS light is coming, the ABS system has shut down itself because of a failure/abnormal signal in one of the components of the ABS.
That doesn't mean that the brake isn't working, the brake works without the help of the ABS such as the lot of Solstices ordered without ABS (in base Sol ABS is an option). I remember dicussions on SolForum what ABS should be useful for.
Under some conditions the brake distances without ABS even can be shorter.
The benefit of the ABS system is that you can't block one or more wheels and that means the car is steerable under full pressure brake.
Another pro is you can't get a brake flat on your wheels.
You can test it yourself: normally there is a discrete fuse for the ABS system or if not you can disconnect a wheel sensor.