Basically bosses can have the effects on them, though certain abilities can be harder to give it. For instance, 2H warrior passive, 50% on critical hit. That works universally on everything - all you have to do is get a few critical hits. Mage is ultimately more limited but they also can take advantage of a lot of stuff in a rather grand way so I feel that balances out.
Either way the simple answer is yes. Though, while I know what you mean there IN1, DA2 doesn't have spellcraft levels, and majority of things are just static %chances now instead of magic resist vs whatever checks for random chances. Bosses, I believe, cut chances in half, Elites is moer like 3/4ths.
For instance Pummel Strike upgraded, is 100% chance if you stun the target. I've actually gotten a stagger off that before I believe when I couldn't stun them. That or the stun disapeared on the boss almost instantly, and the stagger remained. Not sure the duration on Stagger/Disorient/Brittle is effected all that much as they're outside effects from normal skill durations.
or at least, on nightmare, staggering a boss has always lasted long enough to use any combo I wanted.