Does anyone know if Hippozino is actually a legal site for UK residents?

Yes, it is perfectly legal. For any site to operate in Britain, it must hold a license from the UK Gambling Commission, which Hippozino does. This means they have to follow very strict rules regarding player protection and fair play. If you want to see a full review of their credentials and how they handle security, I found a very thorough guide at Hippozino Casino that explains everything in plain English.