Yeah I'd have to agree that NIN and KMFDM don't really qualify as Industrial Metal as most of their music could arguably even be classed as Alternative Dance music. I like both bands and I don't mean that in an insulting way, it's just that they use metal elements in their music like a sampled guitar riff but that seems to be where most similarities end. And that both bands have darker images and themes.
I tend to look at Industrial music as a whole, including the mechanical post punk/gothic rock industrial music like Killing Joke, weird experimentalism of Throbbing Gristle and the cold yet danceable EBM of Front 242.
Also Electric Hellfire Club are well worth checking out if you like Industrial Rock. Die Krupps and Front Line Assembly are also good.
As far as Industrial Metal goes I love Fear Factory. I haven't listen to these bands in a while but I used to like Strapping Young Lad, Nailbomb and Prong.