I agree 100% with the No Heart theory you have! Especially this argument that you make:
Riku mentions in BBS that he knew of a boy who left DI a long time ago. Surely he is a thing of urban legend, and even if Riku couldn't recall the name then and there (to Aqua I think it was?) surely if someone said OX's true name to Sora or Riku, then they would recall him as being someone form there home. But all through KH2 Sora shows no recollection of the name Xehanort, after it is first mentioned to him by Mickey in HB.
This won my support. Great job on the theory!