Well I'll try to answer from my experience. I know that if you're staying at a resort which doesn't have a health club (or any resort for that matter), that you're allowed to go and use the one at the Grand Floridian for a fee (usually $15 per day or $35 for length of stay for one person). Most of the other resort's health clubs are for the use of that resort's guests only (and I've seen people turned away because they were staying at another resort). If you were a guest of someone staying at that resort where the health club is, and you both were going in to use it together, it's possible they might let you, I don't know about that, would have to ask or call them in advance.