Nah, that's all Zakk (except on "Stillborn," of course). If you listen to Sonic Brew, it's there. "Mother Mary" it's probably most obvious. The thing is, back then his clean tone had a "scratchy" exterior. That's the sing of a singer that just isn't strong enough to push his vocals into that clean-only zone. With power, of course. We knew he can do the quieter, more mellow clean style with ease.