Vampire Aristocrat

• WWizards of the Coast2009-10-01
  Official Ruling
  You can sacrifice Vampire Aristocrat to activate its own ability, but it won't be around to get the bonus.
• WWizards of the Coast2009-10-01
  Official Ruling
  If you sacrifice an attacking or blocking creature during the declare blockers step, it won't deal combat damage. If you wait until the combat damage step, but that creature has been dealt lethal damage, it'll be destroyed before you get a chance to sacrifice it.

Rulings via Scryfall