A little extra transmission cooling is no good reason to risk transmission failure.
Correct, I have never seen this happen on a GM product either, or even heard of it, but that's only where factory radiators are concerned. Lots of aftermarket radiators do it when brand new, let alone over time.
One of the things I liked about my auto Ram is that there is no sharing between radiator and transmission. It has its transmission cooler behind the intercooler and nothing else.