Not all hunters and not all the time. There are plenty of hunters out there who hold their coins until they see fit to sell. There are also situations where they dump their coins right away especially if the coin is not doing good or because of the devs and team behind the coin.
actually if indeed they are bounty hunters selling coins directly at the same time it will not make the price a dump, because the allocation of tokens for bounties is very little, only 2-4%. and that won't have much effect