I don't think bounty hunters are the cause of the dumping. Distribution of huge number of tokens to investors in the form of discounts makes investors get a lot of the tokens.  Investors are the real cause of dumping. Bounty hunters usually get almost just a small fraction of the total tokens being distributed.
Joining a bounty campaign can either be worth it or not at all. I will suggest that before you join a bounty campaign, bounty hunters need to do some research about the project and how  feasible  is it to the crypto ecosystem.