Yeah, discovering Nau’s chamber of horrors is meant to strip any illusions about his motivations.

Book spoilers.

IIRC wasn't it the chamber/ship of someone he worked with, that he tolerated? Read it like six or seven years ago, so the details are fuzzy. The impression I kept was that he did a lot of evil stuff not because he relished the suffering he created in others, but because he didn't mind it.

Yes, it was not his chamber, but Nau never wanted one because he kept a pet in the open.

It's both. On one hand, he is aware that one of his valued subordinates "needs" to regularly murder people, and doesn't consider it an issue so long as that subordinate remains productive and is kept in check to avoid "wasting resources".

But there's also a record of him personally torturing and raping one of the captives for the sake of it - which he keeps around, presumably to rewatch every now and then.

Thats right, I forgot about Nau’s enforcer (whose name escapes me atm).

Anyway I think the point remains - after that point, the reader is meant to understand that the emergents self-serving justifications are just that.