Twitter is a great place to promote any product including gambling business but obviously it should be managed well by having real interaction with followes. One of the best way to interact with followers is by having promotion or giveaway as you suggest. With a requirement such as like and retweet will help them to spread the words.
A lot of casinos are making the best use of twitter for marketing purpose. Some casinos offer free spins, cash bonus, etc to random users on twitter who retweet and make comments on their posts. Check the pinned tweet of Punt.com, they had announced $100k giveaway on their twitter 6 months ago. There isn't so much entries for the giveaway, and they haven't announced the winners in 6 months. Punt.com team aren't doing the marketing as they should have.That's their weakness if the continue like that then it would be hard for them to attract new users. And, many of the existing users will also transition to other gambling sites. In this time social media and mostly twitter is very important for promotions, and many gambling sites are taking advantage of the platform by doing giveaways to attract new users to their site. If Punt.com doesn't improve its social media channels then things won't go very well for them.
Many of the sites are spending thousands of dollars for the social media marketing and in return they are getting very good clients that are spending a lot money of their platforms. They know that the twitter is key to success in this age and whoever uses it for marketing purposes gains so many users to their sites that other could only dream of.
