Well, you've got to keep in mind that there's a difference between a Somebody and a Nobody with a heart... Sure they have the same materials, Heart-Body-Soul, but whether the new heart they grow is theirs or not, they're still just Nobodies with a Heart... As Axel so eloquently put it "We Nobodies can never hope to be Somebodies", but they can develop hearts which make them essentially somebodies, just not Somebodies by classification
Think about it like this, let's say Jake is an awesome dude... When he dies, he develops a heartless and a Nobody, that Nobody he creates is a Twilight Thorn... Well, this Twilight Thorn develops a heart (it couldn't but let's pretend) And now consists of a Heart-Body-Soul right? So is Jakes Nobody a somebody? Of course not, that body of his is the body of a Nobody (a twilight thorn specifically), not the body of a Somebody
...
That lengthy explanation over, I believe a few of them developed hearts, and I believe a few of them had Xehanort Hearts growing inside them. The one's I'm pretty sure had hearts were: Xemnas, Xigbar, Saix, Axel, Roxas, and Xion.