Copyright law doesn't care about whether this is "monetizing" or not. He's infringing simply by using JK Rowling's characters; he's safe only thanks to JK Rowling saying that she doesn't mind HP fanfiction as long as it's not obscene and non-commercial.
So the only real question here is: What does JK Rowling think of this?
Sure. My point is, this is all based on her whims, not on any legal definitions. So "non-commercial" in this context just means whatever JK Rowling wants it to mean in this context.
Given that it's raising money for a charities, and that the donations only accelerate the publication rate, I would be surprised to see Rowling object when she hasn't objected to previous chapters.
So the only real question here is: What does JK Rowling think of this?