Does a sacrificed creature count as a creature that died?
Yes. Assuming the sacrificed creature is a Zombie, Diregraf Captain's ability will cause target opponent to lose 1 life. This is because "dies" simply means "goes to the graveyard from the battlefield". 


  700.6. The term dies means "is put into a graveyard from the battlefield." It is used only when referring to creatures.


A card that talks about something that "dies" does not care if the creature is going to the graveyard because of combat damage, a destruction spell such as Doom Blade, because it was sacrificed, or because its toughness was reduced to 0.