Yes they have a right to merit their posters but no offense here it's not the manager's responsibility to give merits to their quality posters it's not their problem that some posters don't get merits and also, if a poster applied to join in that campaign right?
It might not be the CMs
responsibility, then who has then? It is not their
problem, true, its not really have to be a problem, in this case its just going to be an
incentive to the participants for them to even strive more to have quality posts.
Still, its the campaign managers decision on how they will give merits. Its also the responsibility of all the members to give merits on quality posts that they encounter daily in the forum which can also help. Don't just give all the responsibility to a person which they are not accountable. It will just reflecting on how you really eager to have merits over the forum.