Can an ISO 9001 certified auditor perform IATF16949 audits (assuming that the auditor is knowledgeable on the IATF requirements), was geared towards whether any performed audits would be considered valid by a accreditation body.
I think you are asking this question for internal auditor competency. According to article 7.2.3 of IATF 16949:2016 standard, system auditors should have the following information.
understanding of the automotive process approach for auditing, including risk-based thinking;
understanding of applicable customer-specific requirements;
understanding of applicable ISO 9001 and lATF 16949 requirements related to the scope of the audit;
understanding of applicable core tool requirements related to the scope of the audit;
understanding how to plan, conduct, report, and closeout audit findings.
As you know, the basic tools are APQP, PPAP, FMEA, SPC, MSA. In these subjects, it may be necessary to show either the training record or the experience records on the CV.
In addition, Control Plan, FMEA, and related manufacturing process experience are required within manufacturing process auditors.
If your ISO 9001 certified internal auditors can demonstrate the above-mentioned competencies, they can carry out inspections. Apart from these, if there is an additional requirement from the customer's special request, it may be necessary to provide evidence on that subject.