No, you're comparing a hypothetical service to a material service. Sammy isn't exploiting the bar because the bar doesn't pay her. She's paid entirely through tips. If the customers didn't want Sammy getting the beers for them then they wouldn't tip her, along with optional services rendered. The only mildly exploitive aspect of Sammy's work is when she's selling her underwear for a profit. The rest of it is not.
There's another difference. It's a reasonable expectation that someone could call a contractor when something in their house breaks. It's not a reasonable expectation that someone could go behind a bar they don't own and pour themself a pint. If the amount they're paying in rent is enough to cover any maintenance costs then they're perfectly capable of assuming any maintenance costs in lieu of rent. Oskar is providing nothing in your example, he's taking their money to do what they could do themselves and pocketing the difference.
He is not providing anything noticeable because, ingame, nothing in your apartment breaks down. It is not a plot point that a window breaks or the central heating stops working or there's a gas leak somewhere and you need to go to Oskar to arrange to fix it, but that does not mean he would refuse to do anything when these events might take place. My old boss used to rent out apartments above his store, he got money every month but when a roof started leaking he had to arrange for someone to go and fix it, not his tenants.
Sam_Tail is planning to expand Oskar in future versions, but as it is it's a difference in assumptions: Oskar doesn't (yet) do anything noticeable, and while your assumption is that that means he is unwilling to do anything, mine is that it is too early to say as a situation where he might need to step in hasn't happened yet. To be fair, when Sammy can't afford rent his first reaction is not to yell at her or threaten to toss her out, but to give an alternative where she can work off her rent through compensatory labor, be it cleaning or casino work. And these remain optional, he doesn't call in a couple of gangsters to drag Sammy kicking and screaming to the casino in a leotard, the choice to accept is ultimately yours so i'm giving him the benefit of the doubt based on his character so far.
Read above. Not all labour needs to be transformative for it to provide value if it enables transformative labour to continue and or facilitates its compensation. The miniscule tax load of 911 operators was well worth it when my dad needed an ambulance for a heart attack a couple years ago. The tax load that paid for the doctors and hospital was well worth it when he had to stay there for a few weeks feeding and housing him, when they gave him a battery of tests and when they operated on him for a grand total of $60 for only the ambulance. Care workers provide value by enabling transformative labour to exist. Without them we'd lose a worker every time one of them got seriously ill. Oscar does not provide that service, he does nothing that his tenants are perfectly capable of doing themselves. My dad couldn't have marched into a hospital on his own and performed his own open heart surgery.
Glad to hear your father's doing okay.
My point is though, administrative work does add value to a product, even through something as basic as customer support. Landlord is not technically a job, but that does not mean they don't do anything worth being compensated for. You'd have a point if he was a loanshark (someone that uses money to generate more money) though.