Although I haven't been watching CE in recount as much lately as when I first picked it up, the only time I noticed a crit was when I exploded the actual ghoul. This occurred in Maraudon on a solo run for the Elder, so there weren't any outside crit debuffs present.
Ran a few solo oldschool Stratholmes today and used corpse explosion liberally. On really large packs like the flood of mindless skeletons right before Baron, I did notice that CE would occasionally crit. Not just in recount, but in the actual combat log. The crit rate seems to be very very low. Maybe it's only effected by crit on gear or perhaps from just one of our talents? I was 10/50/11 tankspec... and the only +crit talent in that spec is Acclimation, which provides '3% crit to your melee special abilities'... 3% would support the ultra low crit rate... needs more testing!