This question has many layers. You, as the contractor, are responsible for the actions of the outside recruiters. The outside recruiters, standing in for you -- the federal contractor -- are responsible for obtaining demographic (race, gender, disability status and veteran status) for all candidates that they believe meet the minimum qualifications. A best practice is to have the recruiters ask all interested applicants to apply to the ATS, as OFCCP may ultimately have a different determination regarding minimum qualifications.
You can use this OFCCP audit checklist to ensure you're doing what is required to maintain OFCCP's regulations including VEVRAA, Section 503, and EO 11246. Or request a demo to streamline your compliance and recruiting efforts.