There is no such thing as zombie metal, because genres are based on musical traits, not lyrical traits. You can be a thrash metal band that sings about Zombies, but that does not make you "zombie metal," it makes you thrash metal.
The music genre of Zombie Nation is Techno and Electro. Zombie Nation is a German techno and electro project of the Munich, Bavaria, Germany based DJ and producer Florian Senfter.
As far as the material goes, there are rods, robots, race-cars, rakes (?), and rings. If you consider 'Metal' the genre of music, then you could use Rob Zombie.
metal
The genre of nu metal is a sub genre of the hard rock music. Nu Metal basically combines the genre of hard rock with some of it's other genres like groove metal and trash metal.
Rob zombie is considered metal , but most consider his music heavy rock an roll . He is under the heavy metal section in most music stores .
Thrash metal
Industrial metal.
Alternative metal
Their music features elements from classical music and neo-classical metal, to symphonic metal and gothic metal.
rock! and metal
Alternative metal.
metal