I'm not a fan of Dex-Crap myself. I prefer good ol ehtylene-glycol. But both contain stuff that'll oxidize aluminum.
There was actually a post in the Heavy Duty section on GM-Trucks.com a long time ago where one of the guys (an engineer actually broke out the properties of each and their performance, durability, and longevity. The two were fairly neck and neck in most categories. The one thing the good ol green stuff did better was it's thermal conductiveness (or something like that), I.E. it cooled quicker, faster and more than Dex-Crap.
I've seen many a GM motor in the service lanes with Dex-Crap, including one of my own that are well past 100k with the stuff. So it isn't all that bad. The problem lies in that people are told it is 100k coolant. So they don't perform maintanance, I.E. a flush (and/or powerflushing) and re-fill until that point and that's where the damage occurs.