mteal: Yes, I noticed occaisional Wellesian-looking shots too.
There possibly could have been a link with the earlier production that Welles agreed to direct back-to-back with CHIMES AT MIDNIGHT, for one of the CHIMES producers, in order to get CHIMES made, which Jesus Franco (as Harvey Chartrand mentioned above) shot some scenes for in 1965. There are a couple of connections: a lot of the people involved in the production of the 1972 TREASURE ISLAND had Franco connections (one of the producers, Artur Brauner, produced Franco's VAMPYROS LESBOS, and of course Harry Alan Towers and Franco were a team for many years), Welles is credited as having co-written the entire script (under the pseudonym O. W. Jeeves), so it's possible that the production was an evolution of the 1965 film Welles never got around to. If it is connected, it's possible Welles directed some of it. Maybe some of those scenic shots are the stuff Franco did in 1965...or maybe not. Of course, some directors do seem to have improved when Welles was around, so it could even have been 100% Hough, but Hough under the influence of Welles.
Whatever it's roots are, TREASURE ISLAND is certainly an interesting film, IMHO. It's historically important, as the script was the penultimate Welles-written (or in this case, co-written) script to reach the screen, it's probably the nearest it's producers ever got to "respectable" filmmaking, as well as being a case of "When Worlds Collide" (Orson Welles co-writing a script for a producer of lesbian vampire movies).
Welles isn't bad as Long John Silver, a little delirious-seeming in some scenes, but not as roaringly hammy as you might expect. Beautiful locations well-photographed: as mteal said, a handsome-looking film. Very outdoorsy, reasonably entertaining.
Another note: There exists (according to The IMDb) an Italian-language version with different footage: oddly, this is listed under the German-language title DIE SCHATZINSEL (international co-production strikes again:)), has anyone seen this?