Corpse Take lasts for 20 minutes. For your question, yes, I only get healed once even though I killed multiple monsters afflicted by Corpse Take.
Corpse Explosion (the one with Blazing Body & Fire Blast icon) does work. I tested it on Slimes today. Gather some Slimes, cast Corpse Explosion, and kill just one of them. All of the Slimes around the afflicted one will die. However, there is a bug regarding Corpse Explosion. Monsters killed by Corpse Explosion will not count as a kill. No experience and gold gained, the kill count below the minimap won't increase either. Those numbers that indicate how much damage a monster takes won't appear as well. The damage done, though not indicated, is very small that it is hardly noticeable.