Yes.All the websites that offer free spin bonuses to win real cash prizes do so after you have a registered an account on their platform. They do so not only because theywant you to register and try their services, but also because they need to make sure you are legally allowed to gamble online.
Signing up for their player's clubs will get you some free stuff, even if you never play any of the table games or their slots. That's the most free stuff you'll ever get from any casino, beyond that it's going to cost you.