This is about certificates for OH&S (Occupational Health & Safety) management systems. EcoVadis accepts them as evidence.
In Germany, a well known CAB (accredited Compliance Assessment Body) of OH&S management systems tolerated for several years a very obvious non compliance of his client with OHSAS 18001:2007. Seemingly the client certified by that CAB did not like the terms in OHSAS 18001:2007 and therefore kept using the terms of OHSAS 18001:1999, which are less demanding. After some years an employee discovered that. The accreditation body DAkkS initiated a re-audit.
In Germany, at least the big CABs protect employers, not employees. The best OHSAS 18001 audits in Europe probably are run in the Netherlands, where the SCCM auditing scheme is applied.
Bad audits of OH&S managements systems by CABs and by the authorities are a problem for companies like EcoVadis. Certificates provided by accredited CABs simplify their efficiency optimized document audits (remote audits in most cases). But even with well known suppliers and CABs those assessment providers like EcoVadis cannot rely on OHSAS 18001 audits. One way to verify the quality of OHSAS 18001 implementation could be to check, whether assessed suppliers really register and evaluate all incidents defined in clause 3.9 (and clause 3.8) in OHSAS 18001:2007.