My sister-in-law and I both had massages and were told that the discount was good on all services when we checked out of the spa. However, we were told differently on the phone when we made the appointments.
Discounts vary by season, I believe. Keep in mind that, while not all services receive the discount, everyone in your party (staying with you on DVC points) DOES get whatever discounts are available to you as the DVC member. Six of us got facials/massages in November and that discount was awfully nice!