Is ISO 22301 mandatory for audits?

Please note that an ISO management standard is mandatory for an audit only if you are certified on that standard, or in case you have to comply with a law, regulation, or contract that demands the application of the standard during an audit.  

In case these situations do not apply to you, the standard is not mandatory in an audit.

These articles will provide you a further explanation about the identification of legal requirements (the same concept applies for both ISO 22301 and ISO 13485):

• How to identify ISMS requirements of interested parties in ISO 27001 https://advisera.com/27001academy/blog/2017/02/06/how-to-identify-isms-requirements-of-interested-parties-in-iso-27001/
• How to make an Internal Audit checklist for ISO 27001 / ISO 22301 https://advisera.com/27001academy/knowledgebase/how-to-make-an-internal-audit-checklist-for-iso-27001-iso-22301/