1. depends on your location. for example, in the UK you can have a gambling website, in the US it is far more tricky.
2. some online casino's and gambling sites have been known to pay £50+ per lead when you send them sign-ups for their free accounts. it can be lucrative, but the PPL programs come and go so you need to constantly find the best offers.
I have a detailed report on the gambling niche and how to generate an income from it, if anyone wants it just PM.