Nu-metal guys, don't hate me for this. I love nu-metal too. But...
I don't think nu-metal belongs to metal. It doesn't seem to belong to anything, in fact. It is a very experimental genre, fusing influences from everywhere. Ill Nino has Brazilian folk influences as does Soulfly. Then you have bands like Godsmack which are just plain heavy and groovy from start to end, then to Linkin Park which has rap and industrial.
Basically, nu-metal's on its own, since it's a very experimental, fusion genre rather than a subgenre of anything.