I can't help you because I don't have the tier bonus but my guesses are.
You won't proc the bonus if the attack is missed: you have not been hit.
Won't proc form spells or dots: Blizz usually make difference between "hit" and "Spell hit".
It will proc if you are stunned or attacked from behind: you are being hit for sure.
Can't help you about dodge/parry/block. Im confident that block will proc it, but the other two :S