Yeah, even after the DoT-stacking patch of 2002, various dot/debuff combo spells still didn't stack, only pure DoTs. For example,
Dooming Darkness wouldn't stack if cast by multiple players, since it has a snare component. But
Ignite Blood would stack (after the patch), since it's just a straight DoT with no debuff.
I suspect
Asystole does not stack, due to the STR/AC debuff, but I could be wrong.