Make sure they bleed all the air of of the system after a full flush, and as the others said, you can use another Antifreeze without issues, I have heard of Prestone Extended Life, and Zerex G05 are good replacements.
To be honest IMO as long as you have the coolant serviced regularly, and there is never any air left in the system, then Dex Cool normally does not cause any problems, I have used it for 136k on my Park Ave, and the only thing anybody can say could have been caused by using it, is my Lower Intake Manifold Gaskets failing, but I personally think that is because of the heat, and that the frame of the gasket was made out of nylon 6,6.
My radiator fins look as good as new, and every time I service my coolant it looks nice and clean.
I won't elaborate anymore, because the Dex Cool argument has been had more than once, just do some google searches.
2006 Pontiac Grand Prix GT with SC
1996 Buick Park Ave NA