DoT's can crit, this was confirmed a long time ago. Real simple to do. Go put a DoT on a target and watch the floating damage. Occasionally, the tick will spike, this is when the DoT has crit. My Bio II ticks for 88~90 damage every 3s, and occasionally spikes for 120~130 damage. I'm sure there's a video somewhere of this if you really desire more proof. Needless to say, Critical Hit Rate is (in most people's opinion) the better stat to build your gear with. As a SMN and BLM, I go INT > Crit > Det.