Cheaters will always find new ways to abuse the system so it is very hard to get that under control. I don't think these cash drops really gets the attention of new users, it is more a way to reward old users. Personally, I don't get why Twitter is still popular and that a lot of casino really use it. It is full with bots and I really doubt if it is really so effective for marketing.
If we talk about bots, it can be in anywhere in the internet including most other popular social media. Why Twitter is still a good place to be used as marketing, because there are still many people use twitter all around the world. I can even say that Twitter is the most friendly social media for gambling activity compared to other social media, this is why many casinos use it as one of their main target of marketing.