You are getting a couple things wrong.
Bolded: He is not. You keep presuming that a crime is happening with no basis for it whatsoever. If an artist hires a gardener, the gardener is not part of the artistic community because he works for the artist. Bolin was hired to protect the guy as a citizen as far as he knew, not to cover up any crimes. Even if there is a crime going on, Bolin seems entirely ignorant of it, and that makes him innocent of being an accessory. If the police had come upon the situation, they might have taken him in on suspicion, but if they tried to charge him with anything, it'd fall flat.
You've also got the original comparison skewed. Your saying that if TTT guy was doing something illegal and bolin was gaurding him knowing that he was doing that, which si not the same as a person in a dark alley. Which, yeah, I'll agree with. That's not whats happening though. Bolin is just guarding this guy who, as far as he knows, has committed no crimes while he was in his service. Then the Equalists come and are about to mutilate him.
Bolin is as innocent as a person who gets stabbed in a dark alley, because he is being assaulted simply for being in the wrong place at the wrong time, having committed no crime whatsoever. He shouldn't have been there, but that doesn't make him guilty of any wrongdoing. What the difference between these two is that Bolin might LOOK like he is an accessory to this stuff, but the appearance of wrongdoing is not wrongdoing itself.