Depends on your point of view! I personally see Ocarina!Sheik as male, for reasons I've outlined here
. Having said that, seeing Sheik as Zelda works as well, although this is specifically for Link/Sheik - in the manga, for instance, the dynamic between Link/Sheik and Link/Zelda is totally different, so no matter what your view of Sheik is, I'd classify the two as seperate.
So basically, this is for any variation of Link/Sheik in Ocarina, no matter what your views
. If you want to view it as an extension of Link/Zelda, that's fine, if you want to view it seperately, that's also fine.
(Although I should point out that Zelda being a girl doesn't necessarily make Sheik one - if it's a disguise, it's explicitely a male disguise, looks physically male, characters refer to him as male, and the whole... 'Zelda = female, Zelda = Sheik, therefore Sheik = female' doesn't work. Like... 'Zelda = blue-eyed, Zelda = Sheik, therefore Sheik = blue-eyed'. When we know that's not true.)