OpenLDAP is a standard LDAP server that adheres to RFC-2307 compliance, so it works fine with ONTAP as an identity management service for users and groups.
In ONTAP, you configure it by creating an LDAP client in the SVM as per this:
https://docs.netapp.com/us-en/ontap/nfs-config/create-ldap-client-config-task.html
OpenLDAP configuration in ONTAP is simply knowing how to bind (login) to the LDAP server (anonymous? password? certificates?) and what the LDAP schema is for lookups. For OpenLDAP, it's generally RFC-2307.
This doc covers creating LDAP clients in SVMs:
https://docs.netapp.com/us-en/ontap/nfs-config/create-ldap-client-config-task.html
This TR covers LDAP in general and shows sample configs (with a focus on AD LDAP and FreeIPA) and should give you some idea of how this is configured and commands to test it out:
https://www.netapp.com/pdf.html?item=/media/19423-tr-4835.pdf
