There is no fee for members, though non-members are expected to pay (not sure how much). However, when we were there just a few weeks ago, no one asked to see our blue card.
I am pretty sure that anytime the non-DVC members are staying with a member on points, their room card/i.d says DVC member and they are afforded same privileges as members (i.e. free use of fitness facilities, spa discount, etc). My husband liked the SSR fitness area and I enjoyed hanging out at the pool while he worked out.