Well, the dwarves were aggressive and war-like, just not naturally evil nor particularly hostile. They were tough for Sauron to tame, because they didn't take well to be dominated by others.
I would put their lack of Numenorean-esque "Imperialism" down to they pretty much wanted to be left alone to their underground halls and mining. Imperialism requires a certain hubris that means "my particular race is superior to yours and you should therefor adapt our customs/ways of life, because your ways are inferior." This is exemplified in the Numenoreans who believed they were the superior race of Men and were bringing "light and teaching" to all other men.
The dwarves don't have this superior hubris, but they're still extremely warlike and aggressive:
Quote:
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A warlike race of old were all the Naugrim, and they would fight fiercely against whomsoever aggrieved them: servants of Melkor, or Eldar, or Avari, or wild beasts, or not seldom their own kin, Dwarves of other mansions and lordships.~Of the Sindar
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And they didn't like orcs/goblins very much either.