Not sure about sites that are specializing in this niches. I have in the past targeted similiar key phrases with landing pages specific to these niches and the conversions where less than more general terms used on Overture.
In addition, the traffic was obviously very small and I concluded early that these niche markets may bring the odd player but they are better as a compliment to an existing general casino site than a stand alone effort.
Things may have changed in the last 1-1/2 to 2 years since I tried this but I won’t be targetting these niches again anytime soon.
If you can find different results then all the power to you cause you made a niche market work for you!
Kevin 11