I could be wrong, but I'm fairly sure it only applies to skills that specifically state that they deal higher damage when the target is below a certain percentage of health. I do not think that those passives you mentioned apply.
Skills like Steel Tornado or Executioner come to mind. Not entirely sure, but Poison Injection might work too.
Steel Tornado, Executioner and Poison Injection all work. Poison inject is my favorite for it as it seems to work the best. You either need to have sheer venom on both bars or wait for the poison dot to tick if you only have it on your bow bar. Or fire poison inject and bar swap if you only have sheer venom on the other bar.