You know what's great about Jack Black? He is a parody of himself. Think about it, his acting is over the top, the roles he plays cater to this, and if you just listen to him sing you realize that there is nothing "serious" about what he's doing.
This entire tribute album is reasonably good, so if you have the time I'd recommend listening through the whole thing. The Judas Priest cover and the cover with Corey Taylor are really good.
I really am not too familiar with a lot of Dio's own music, just some of the stuff he did with Sabbath. Still though, if you're a fan then this album is good.