You will need to be resident to get membership but you don't need to have membership to get in the club, you can pay at the gate. Membership makes sense though if you live in Rehab as you are likely to use the club on a regular basis, and it will allow you to use the private pool when it is open.
(Unless they have changed the rules in the last couple of weeks, which really wouldn't surprise me: they make them up as they go along!)