I think that this manager checks absolutely all posts, no matter where they were written. As mentioned earlier, yahoo has access to the yobit panel and before evaluating bitcoins, he evaluates the quality of posts.
Yahoo has no any power to evaluating bitcoins in yobit's participants account. He simply only has the power of ban, if s/he already spamming 20 posts in a day, it will be counted on their yobit's account, yahoo can't do anything about that.
But how can people make 20 posts in a day without spamming?
Seriously? You joined this campaign with a newbie account?

Obviously nope. He might be joined with his other account.