That says unsigned artists must register with one of those four services. From their web page, the first one listed (https://www.recordunion.com/) is a digital distribution company that charges under $15/year to interface with an online store on the artist's behalf.

If an artist is signed to a label then it's on the label to have a working relationship with the online stores and streaming services.

None of those companies are labels, they are all distributors - I suspect in short order you will see more of the major distributors on board, e.g. The Orchard, InGrooves, and possibly some of the commodity style ones too like TuneCore and CD Baby