Couldn't you argue that not working at the club, and subsequently not allowing her mother to receive August's money for her medical care, would be the morally wrong thing to do? All Hana does is serve drinks. She doesn't abuse the girls, she's not involved directly in the activities; she's just the bartender. She makes it very clear that she's 100% only there because of her mom and, the fact that she's doing something that she is vehemently opposed to for the sake of her mother, makes her even more virtuous in my eyes.
I see where you're coming from, but sorry, I disagree. I once heard "I've got a mortgage" referred to as the Yuppie Nuremberg Defense and it makes me chuckle every time I remember it. Everyone has financial needs that, to them, are incredibly important, and seem to be worth bending certain moral rules - but if everyone operates on that basis, society crumbles (or at least weakens).
Nor do I think it's a defense that Hana plays only a minor role in the operation of the club. The club requires a bartender to function. It's a minor role, for sure, but a necessary one, and most criminal organizations are built on a collection of people like Hana who console themselves that they're only playing an auxiliary role in the crime. "I just dispose of the bodies", "I just wash the dirty money", etc. Participation is therefore evil, although of course of a relatively minor evil variety.
As an aside, speaking as someone who enjoys the male dom kink, she's a significant "catch" from an employee perspective, because she's an attractive, dignified woman being made to do something she finds disgusting for money, just like Veronica. Her very dislike of her own job - while still continuing to do it - is a turn-on. She's a featured attraction, in some ways, in a way that a person who has no dignity in the first place, like Felicia, is not. I'm not turned on by rape, but the phrase "you can't rape the willing" is analogous to what I'm talking about.
And sure, the club
could operate without her, but the same is true of most criminal enterprises. "Somebody was going to sell drugs to that junkie." Being a good person requires acknowledging that it
may be true, but it doesn't mean you have to participate. Your soul is at stake, and you have a responsibility to set a good example for others. See e.g. Russell Crowe's character in
American Gangster, who refuses to take dirty money that his corrupt milieu actually
expects him to take and punishes him for not taking.
I note for anyone reading this out of context that I'm actually playing the evil route and having great fun doing it. This is just an unexpectedly enjoyable discussion about theoretical ethics.