You can call the FW desk (ask for the FW Marina number) and confirm but I think the "Admiral's Plan" went the way of Davey Jones' locker several years ago. As with all things that were in the consumers' favor, Disney shut it down years ago I think.
That "deal" is long gone. At this point, the only watercraft discount for the general public that I am aware of is AAA (I think it's about 15%)... but every little bit helps. Happy boating.