User blog comment:Aizen.sama/Are Espadas, Vasto Lorde(s)?/@comment-1393830-20100420214452

Yes but Urahara did not know how to use the hogyoku. Aizen states that he knows how to use it much better than Urahara and thus could have granted Tosen a perfect hollow form complete with ressurection, the vizard were given imperfect hollow forms