In most cases. What does Oscar actively do though? Facilitate utilities and that's it. There's no evidence he's performing active maintenance. He isn't cleaning, Sammy's optionally doing that. So he's provided a 1 time service of furnishing, has set up the utilities which Sammy could've done herself, and he gets Sammy to clean the place. He isn't actively doing anything to earn these residuals. There's no service he provides that couldn't have been performed with a housing coop of Sammy and the other renters other than exploiting the land usage.
Sammy doesn't get paid by the bar, she's paid entirely in tips for her service. People pay her as they feel her service is worth to them. If anything Sammy's being exploited by the bar for free labour in exchange for tip revenue.
But the point still stands that she isn't
producing anything with her efforts, except maybe cum stains on the floor. She's providing a service, certainly, by receiving payment for doing something so the people she's doing it for won't have to go through the effort of doing it themselves...
...Which is exactly what Oskar is doing. In case of a major repair Sammy notifies Oskar, who then seeks out a contractor and makes arrangements, rather than Sammy having to put her effort in over a week or two, then negotiating with her flatmates to put enough money together to repair it (which is harder if only a few apartments are impacted by the necessary repair) leading to arguments and, eventually, a breakdown of negotiations and the place looking like Haven a few years down the line. That is what you pay for and, unlike bar work, it is a previously agreed upon sum rather than 'whatever they feel like'.
By your logic, you are being exploited by 9-1-1 operators because a portion of your taxes is going towards paying them, despite them not producing anything and you personally haven't had to call them in the past couple of months. But they are there when you need them, and it is that availability as a service that you are paying them for.