First off, let me say that DoT crits are NOT YELLOW, they remain white.
ALL DoTs can crit, however they are divided into 2 categories. DoTs that can crit for each tick individually and DoTs that crit per cast, meaning crit is considered for the initial cast AND when the same cast is applied to a new targets, so the same cast can be a non crit on the first target and then crit on the second (for spells that jump like Haunt or Loctus Swarm). That means either all ticks crit or none.
Corpse Spider (Spider Queen)
Firebomb (Firepool + Pyrogeist)
Gargantuan (Big Stinker)
Grasp of the Dead (including Rain of Corpse)
Mass Confusion (Mass Hallucination)
Plague of Toads (Rain of Toads)
Spirit Barrage (Phantasm)
Wall of Zombie
Zombie Dogs (Burning Dogs)
Hex (Painful Transformation)
Plague of Toad (Toad of Hugeness)
Poison Dart DoT
Another thing I noticed is that sometimes you get a slightly different tick. I do not know when or why this is the case. It's slightly more damage but not enough to be a crit.
PS: With low APS Resentful Spirit is quite the trash clearer as it has a very fat cast animation (in comparison with slow-mo bombs) does enormous damage and spreads upon death and yields additional DPS for single target in combination with darts. Also flies through walls and is mana friendlier. All in all one of the best all-rounder spells, gotta keep it for a while and test how it fares in a group environment.