You can participate in these campaigns, but these campaigns are for reputable and skilled users. Like DT members, moderators and people that are respected in the community, they deceive to be paid in real cryptocurrencies.
No, such bounty are not for deceiving or mainly for reputable members of the forum. The last time I checked anyone who's a good posted can participate in the bounty that pay in Ethereum or bitcoin and I think the reason behind this switch of payment was because some project owner believe bounty hunters are behind the down in price of most new project.
I do agree with you and bounties are sometime seems as the reason why some tokens get dumped after listed. I have seen tokens like ENK and four pillar get dumped just by the bounty hunters and uptill now those projects could not recovered.
Paying bounty in ethereum or bitcoin will reduce dumping of those new projects that cannot withstand the pressure from dumpers.