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/this tool will help the site improving their giveaways . so anything that will make them find abusers is literally a big help.
and also maybe extending other giveaways not only in twitter like at least telegram or facebook (sorry if I missed something that already running)
I am willing to bring more support to those initiative .