Can Someone Really Be a Very Low Empathy Narcissist and Not Know It?
Yes! Narcissists won't often know much about their state. Just look at Bernie Madoff in this article -- he feels very uncomfortable about the idea that he might be a sociopath. Sure, he knows he did a bunch of bad things. But at the same time, he knows that deep down he's good inside. That's that typical narcissist self-deception; he's trying to avoid any shame, or even any awareness of shame.
Malignant narcissists will often do terribly cruel things to others. They'll tell themselves that the other guy had it coming to him. For a classic malignant narcissist, see this story.
Like Madoff, the malignant narcissist in that story, Raucci, thinks of himself as a very good guy. He really puts himself out for his friends. In a sense he's correct, and that should be the clue that he isn't a sociopath. Were he a sociopath, he wouldn't take other people (and whether they are with or against him) so personally.
Sociopaths aren't nearly as dangerous as narcissists. Narcissists get on self-destructive crusades, because it makes them feel good. Sociopaths avoid crusades, because crusades are expensive.