In general the more creditable bounty manager will benefit the project at the end. It will attract more bounty hunters and investors. Good bounty manager will do their due diligence and make sure not risk their reputation.
That is just the idea a lot of project owners do not understand. These days, some bounty managers have been able to build their reputations over time, have so many followers within the community who are bounty hunters and when they are managing a project, it makes it easy for the project to get projected out the more and help build community faster and that is not something that would easily be gotten with the kind of incentive the OP is coming up with and at the end, he might just end up getting shitty managers anyway and the whole campaign ending up not effective. If he is smart, I would recommend him to just go check out the likes of Yahoo, Sylon, btcltcdigger and few other ones that are well known with bounty management within the community.