OW claims to have art from several artists, though I don't recall it being particularly diverse. Some games have a mish-mash of art from different sources (all with the artists' permission, no doubt)
I don't quite know if this applies, but LOQOO has an option to select western/eastern art styles.
Getting a different artist for every scene seems like it would be good way of transforming your project into an unmanageable mess. It also makes it seem like you have stolen your artwork.