Someone can correct me if I misunderstand, but I always took that to mean you can be any align and be a follower.

It means that if a goodie or cabalmate bad mouths you, and you're a goodie, you still gotta kill them.

Doubtful.

In answer to the first poster's question, a character can be of any alignment or class, though some will be harder than others (like orc, healer). Paladins, due to their Code, will also be a tough row to hoe.

There was a situation with a fort paladin who followed me when the Marshall blackjacked him in jest. No, an Akresius follower should not let that go. Yes, I would expect blood to be spilled, even between goodies. That can conflict with the Code, which causes paladins problems.

As far as badmouthing goes, I'd expect an Akresius follower to handle in an appropriate way depending on their alignment, ethos and role. It could be stoic ignorance or bloodshed, whatever best fits the character.