Onehash does have this kind of feature but it's just an option for the bettors. If you want to register, it's okay but if you don't want to, you have an option to deposit anonymously and you will be given a certain bitcoin address to receive your winning. And after that, the deposit address will be given to you so that's how you bet without any registration. You are not enforcing your gamblers to use it but you are making their lives easier by providing an option.