CASOC clubs are not allowed to discriminate on membership (except for contituent clubs). So anyone is allowed to join the Jewish or Greek society, even if you are not Jewish or Greek. Though usually, if you're willing to pay them $5, anyone will gladly take you. I had a friend who was an active member of the Chinese Society because he liked their parties, but he wasn definitely not Asian.
The only exception is constituent societies. They are clubs where everyone from a school, faculty or college is automatically a member. With those you become a member by being a member of the school/faculty/college, you don't join per se. But even then, you can usually still go to their events, so it doesn't really matter.
Oh, and go Hamish and Caitlin!