User blog comment:Darknesslover5000/What happen to Souls who are by Hollows?/@comment-1351982-20100510034803

I think their souls are trapped within the hollow and when the hollow is slain and purified of their sins, all the souls the hollow has eaten can pass on as well. However if they are not purified(ie. killed by a quincy or killed by an arrancar or any other high ranking hollow) then all of the souls are obliterated from the universe, that soul or souls no longer exist. When Grimmjow killed Luppi, he did not cleanse him like a soul reaper does, he just killed him. So, since an arrancar or menos class hollows are a collection of thousands of souls, all those souls were destroyed including the dominant soul being Luppi's main personality. When Byakuya kills Zomari, Zomari turns into ash, the ash is probably the pure concentration of souls passing on. So the answer to your question is as long as the hollow is purified with a Zanpaktou they will pass onto soul society.