Disney-Nautifan
No Nautilus submarine from 20'000 Leagues Under The Sea has ever been displayed, or seen at the Backlot tour in Disney's Hollywood Studios. When I went to WDW last year, I asked two cast members at Epcot about the submarine that was backstage.
They said that they moved it behind Mission: Space, but in my opinion, I think the information is quite inaccurate, and I believe that is has been behind Soarin for about 5-6 years, and it is probably still there.
About the Nautilus being at Disney's Hollywood Studios does have some basis of true fact. When I went the first time to WDW in 1999, I did see the remains of a Nautilus submarine from the attraction sitting as a static prop in the Pearl Harbour water tank area of the Backlot Tour. It was a very large green vessel with huge wheelhouse eyes, and appeared to have been cut at the dorsal fin, as no tail or rear was visible.
Unfortunately, by the time I went to WDW for the second time in 2002, it was gone. It was possibly removed in 2001. Other Nautili that I have seen around the Disney theme parks was a huge model that used to be in the Living Seas in Epcot, and one that is currently displayed in Walt Disney: One Man's Dream at Disney's Hollywood Studios. I saw that one last year (in 2008).