Evil Humans (like the Bomber in the Chad/Canary arc) can get sent to hell after they become hollows (and I assume if they didn't turn into a hollow either), but Hollows usually end up in SS if they were purified.

Rukia's explanation about the balance and how Quincy's posed a threat to it didn't seem to include hell, so now that you mention that I'm even more confused about tthe whole balance thing and where Hollows fit in.