I've never tried using any DoT so far but I've already had Vexing Mordinia cast on me (lifetap over time, roughly 1.2k dmg over 54 secs). After the end of the DoT's duration it simply poofed as it should, but that could as well be because of the two components of the DoT which are:
-DoT for 1.2k dmg
-Heal over time for the same amount
It could be possible that this DoT wears off whenever the beneficial part of it wears off, making lifetap DoTs the only working DoTs currently.
By the way, it seems that most affliction type spells don't work/work well for the time being (slows don't seem to work, but Malo seems to work). Main focus for the devs at the time being seems however to be to get melee working in a manner as close to EQLive as possible, and that is already a tough thing to do if you don't have insider data...
Wait and see, so far the work done is huge and gets more promising as time passes
.