These things always bug me especially if they are pushy, when we bought our third used fifth wheel of a dealer they included supposed free camping at an outfit like this, but it just did not seem worth it to take advantage of the days we could get and to find the time to do it, so we gave up and did not go and therefore did not have to deal with them trying to interest us in taking on a membership.
I stuck with just calling around and booking spots, or reserving a week or two trip ahead of time.
Have relatives up in the osoyoos Rock creek area, keremeos is nice, been through many times.