reread it again, he can't be corrupted by enteracting with them. He can get whammies just like anyone else. But that's besides the point, nothing was done to him to compel him, not on the mental level.
*Lash would not needed to have died otherwise.
I'm not sure what you are saying. Harry was aware of what Vittorio was doing with his attack, he wasn't compelled to nothing. He knew he couldn't do anything, or at least at that point because he had no clue that he was a star born and had power over Outsiders.
Lasciel/Lash then tried to tempt him to take up the coin so he could fight them. Harry refused, he didn't want to be a slave to her, he'd rather die or go mad with his friends. When he doesn't give in, she agrees that Lasciel doesn't deserve him, then she explains to him that he can fight them and had before when he was sixteen. Then she took the psychic bullet for Harry and he was able to move and fight.
They can not or he is just better at resisting it?
Both I think, it is like when he and Eb fought the cornerhounds. Eb knew about fighting them, but they were afraid of Harry and he was actually able to see what they see when they see him.
What makes Outsiders so bad ass is their psychic attic. And they did make an effort to recruit him, or Sharkface did in Cold Days. Harry is able to see through that and not be influenced.