I'm the one that used the Redline fluid in the trans. I don't believe the fluid caused the whining- everything is still normal, and the whining went away as the weather got nicer (warmer). Heck, it's possible that the fluid just needed to break down a bit. I'm not concerned. Redline is also going into my Z06's transmission soon, very popular among Corvette owners.
That being said, if I were to do it again, I'd stick to OEM fluid for something as intrinsic as a Cadillac transmission. I can't say for sure whether the whining was an existing issue or not, as it was my first winter with the car.
I also recently changed my front/rear diff and t-case oils with Mobil 1 stuff. No issues thus far.