Well, whether or not he's a spirit I don't think will create much involvement with whether or not he's sympathetic. I think it's likely (human or not) that Amon himself will be basically unsympathetic and without mercy, but chances are someone relatively close to him in the movement won't be.

Statistically leaders and people seeking power are more likely to be sociopaths (or at least, near it) so I could handle him rolling either way to be honest. As long as the people within the movements don't turn out black-and-white in good/evil setup? I'm basically fine. I feel like some people close to the old gaang might turn out to be bad guys, so :S