I am sure that as a big gambling site, Duelbits has very strong tools to detect cheat on their website. If they can not detect cheating activities, their business will run out of money soon because cheaters will not stop if they can cheat and get money.
Thats dust amount compared to what Duelbits is making for sure and while there are lots of people using bots to claim those, pretty sure that the number of like and retweets they got on those twitter giveaways are pretty worth it. If a tweet has high number of likes and retweets, the tweet could ready even higher number of impression especially to new unique potential player