Do dead Adventurer's count?
Unless the Haunt specifically says to not count dead adventurers, then you should always include them when calculating goals and other numbers.

And as long as the Haunt says number of adventurers and not number of heroes, then yes, the traitor would receive 4 cultists.

From the rulebook (page 13 under Playing the Haunt):


  Certain haunts require something to be done a number of times equal to the number of adventurers or heroes. Unless the haunt states otherwise, that number includes any adventurers or heroes who have died during the haunt.