Can confirm, I just don't 'believe' it. I do not think that Amazon was knowingly employing neo-nazis.

They benefited hugely from this and I have to this day not seen a public commitment to change things to make sure this does not happen. Even if Amazon was unaware of what they were doing, the fact that afterwards they mostly just papered over it and went on with their lives lends it a tacit approval ("don't get caught again"). If you don't see how this makes them evil, I think we just will never agree on it :)

How did they benefit in any way? ( I read the article but didn't watch the documentary).

It sounds like they needed security guards, and the firm they hired turned out to be one that liked to play fascist dress-up.

Did they benefit more than if they had hired normal security?

The firm kept slaves (took passports, no pay, etc) to do the work in the warehouses that were guarded. Free labour is very cheap, that would be how they benefited.