DexCool is actually a licensed name from GM that indicates the coolant has met their longlife coolant specifications. It's not really a specific technology.
GM had some coolant underfill problems that, because the radiator had no cap at all, like Vipers, and the plastic fill reservior looked full, like Vipers, the owner never suspected problems until it overheated. The field fix was to flush and refill with green, which "magically" cured the problem. (I believe this was in smaller GM SUVs.) Of course filling the system completely didn't have anything to do with it.... The overheating caused severe deposits in the cooling system so just filling up didn't cure the problems due to plugged passageways. So DexCool products got a "reputation" that's been hard to overcome. Consider that it also puts several other green coolant companies literally out of business, and the competitiveness has been at times quite ugly.
Similarly, mixing the two has for some reason caused people anxiety, yet there's no problematic issue not to. There are some laboratory bench tests that were designed long ago to evaluate (green) coolants before pink coolants existed. In these specific tests, pink coolants don't always look great, because the test is measuring something the pink coolant doesn't do. Field performance has always been very good.
As Ron says, the resulting protection is a mix also. Remember that the green coolant works by plating out the additive very quickly to provide a protective coating, so the additive reserve is close to nothing in a short time. The pink coolant works the other way; it only attacts corrosion sites when they show signs of starting, so the additive is available for a much longer time. Hence the 2 year change requirement for the green and the 5 year/150K mile recommendation for pink.
Besides watching the development program progress, I now own a Dodge Intrepid that used recycled glycol with the extended life coolant package for most of it's 147K miles; and having seen the insides, it's fine. Extended life coolant has been in my '92 Dodge van and '96 Dakota since new, in my '94 RT since 20K miles when I got it (now has 60K.)
I'll repeat myself a little and point out that the "bad" news seems to come from competitors or those that hadn't gotten the full story about some problem, while the "good" news is in the technical literature (Society of Automotive Engineers technical papers.) So yes, I think it's a safe, goof-proof, fill and forget product.
(Maybe it was that pink coolant that helped my AX times...)