though if you think that the twitter contests main goal is to attract engagement (farm) then the bots aren't such a big deal, unless they start undermine credibility on the company too much
Partially they can check Twitter farm accounts and verify their quality by audit scores. These sites are not perfect but a company can use it as part of their toolkit to reject low quality accounts and increase effects from their marketing campaigns.
https://twitteraudit.com/https://www.followeraudit.com/