The outcome of a 'no downvote' policy is determined by the willingness of people to participate in it, combined with the quality of the admin team's work and perceptions. If they do everything that's necessary to maintain ethics and to protect the rewards pool in an biased way then it can succeed imo. By having a clear moderation policy, there is at least a chance that the result will be better then existing solutions - but, yes, it's all being run by humans at the end of the day - so it's all possible! ;)