It is possible, and helpful in some situations. For instance, for Hydross resist sets, it is quite difficult to stay crit immune and build up maxed out resistance. Resilience is a cheaper stat for crit reduction. The reason Druids use more resilience though is because defense only benefits them in added chance to be missed and dodge chance, in addition to the crit chance reduction. Agility is a better stat for them, because it provides armor, dodge, and crit. Warriors tend to prefer defense because it keeps avoidance above a minimum to aid in crushing blow prevention via shield block.
The easiest way to calculate it is to open up the "Defenses" tab in your character sheet, then add the numbers given under "defense" and "resilience." If they add up to -5.6% (Druids get 3% for free, so 2.6% from defense and resilience), then you are immune to crits against a raid boss.