User blog comment:Silver-Haired Seireitou/Sake Time with Sei - Can Arrancar Use Kidō?/@comment-1493741-20140413171315/@comment-1493741-20140413201041

I'd disagree because Hollow abilities, beyond Cero are never expressly stated to be either formed by Reiryoku or Reiatsu, only Arrancar techniques are described as such, those techniques also typically "bathe" the user in some way (Bala forms around its user's hands, Hierro is a constant coating over their body) and as hybrids, they don't really stress the dominant, uh, "theory" behind the normal Hollows.

That, and at the same time I'd believe manipulating Reiatsu requires some modicum of skill and intelligence beyond base impulses, not many characters in the series even do so, with Zaraki and Genryusai being the only two that spring to mind among Shinigami and the Arrancar as already mentioned.

As for Gran Rey, Cero itself is supposed to be a concentration of spiritual energy, Gran Rey would be the same thing on a much greater scale, the amount of energy contained within distorts the space around it, a similiar process could be explained for Kurohitsugi, so much power flows through the interior of the spell that space and time is distorted as a result.