Oh come on! Bitvest is the worst campaign I have been a part of. They are basically paying people to spam forum with load of useless messages. And the payment is so low I can't believe that there are still people willing to be in the campaign.
Its none of your matter if they pay low to the signature campaign participants. They have hired a good manager and i don't think anyone who spam can remain in that campaign. If you see any spam by those participants you can highlight them to the campaign manager and he may take steps if your observation is valid.