"Required" by what? Your service agreement may say something about what you will do for the client, so that'll be required. For IRS purposes, i don't think there is a requirement to have a report on testing. The requirement is that you pass all tests. Passing is "required", reports are not "required". Of course not passing is bad and correcting is good and way easier if corrections are made within certain windows that you'll only know if you do the test. So the TPA industry is built upon performing and providing reports as part of the "policies and procedures" the Sponsor has in place.
I have seen each unrelated employer treated as a single employer for valuation/reporting purposes and complete report/valuation packages sent to the whom the TPA was asked to send it. That was sometimes the Plan Sponsor (they got all participating employer reports and did what the wished with them) and sometimes the adopting employer level.
Clear communication of expectations reduced to clear service agreements (TPA to PEO, PEO to Participating employers) lead to what's required, which to my mind should align with what's useful.