There have been suits over this exact issue, for example,
https://www.nytimes.com/2016/07/02/business/unitedhealthcare-sues-dialysis-chain-over-billing.htmlThe suits were over dialysis companies actually paying the premium for private insurance. Perhaps DaVita has found a way around this.
Shifting gears a bit, there was an effort on the part of DaVita (I think) to start a chain of concierge-style premium dialysis clinics that would provide a more pleasant atmosphere with extra non-medical services. This was to be available on a monthly fee basis (insurance or Medicare would continue to pay for dialysis, the patient would pay a monthly fee for premium services). I wonder if this may have been what they were talking about?