Seeing your post I did more digging. You said it well, kinda sorta they do. But not quite in the sense we think of for TV. In fact it wasn't clear "programmers" even get the use for free necessarily but in some cases yes. It's just about what you posted, they are supposed to allow outside programmers and set aside 5% - 8% of their spectrum. But thinking that meant completely free for the applicant may not be correct.
No channel has to be received without a subscription and as I noted none are. That alone makes it dubious even if there are any channels that were mandated that they are truly getting anything. Compare that to Satellite radio where those channels are in the clear. And many of the possible categories may have to pay but at a reduced costs, while it looks like there are some categories that could in theory be put on for "free." Why the quotes for "free?" Because from what I can get online they still had to link at their cost to SiriusXM. Also it appears SiriusXM had any final say in what gets on meaning it had to fit their idea of varied programming that hopes to attract listeners who want a wide choice. So if what was being proposed already existed they could say no.
Again, you phrased it well, kinda sorta.