when you say 'universal coolant' can you be more specific on the brand and type? I myself have seen alot of this 'extended life' 50/50 mixed coolant (or the purple or pinkish looking stuff) being used in the place of the mfg's recommended type and its being fed to us that it is compatible.
But as you mentioned, i have seen tech's mixing it with these other coolant types and it does cause alot of corrosion, rust like buildup or 'mud' as i call it creating clogging in systems and so forth.
And of course if anyone has ever dealt with dexcool, NOTHING will mix with it period and it is highly corrosive if not changed out on the recommended schedule.