Since Ichigo has shikai / bankai, it's pretty safe to assume nothing happens to that ability when a shinigami is turned into a vaizard. Whether arrancars gain those, is another thing. I guess it depends on how complete their zanpakutou are. If they are perfect, then there should be no obstacles for acquiring shikai / bankai, at least for vasto lordes. The lesser hollows might be too stupid to acquire anything that sophisticated. Especially bankai.