Can you revive the creature you sacrificed with Hell's Caretaker?
Doing so to re-trigger "enters the battlefield" effects.
The steps to casting a spell or activating an ability are:
The sacrificed creature is only moved to the graveyard in step 5, but you need to pick a card in the graveyard in step 2.
You have to choose a creature to 'target' at the time you activate the ability (Rule 601.2c). At this point in the activating process, you have not payed the cost to active the ability(rule 601.2g), so the creature you would sacrifice is not in the graveyard and is not a valid target.