Do you still have a valid support contract with NetApp (Not for those systems) with any current Hardware that you are using? Is there a NetApp Account Manager assigned to your company ? If you have a valid contract, and you are able to access the support site and open a case (not-technical), then you might want to post your query and get a reply.
These are the kbs related to sanitise that you may find handy.
If you have a valid support account, this kb explains this. (The licenses are free)
https://kb.netapp.com/onprem/ontap/hardware/Disk_Sanitization
Disk Sanitization - NetApp Knowledge Base
https://kb.netapp.com/onprem/ontap/os/Using_disk_sanitization_to_remove_data_from_spare_disks
Using disk sanitization to remove data from spare disks - NetApp Knowledge Base
https://library.netapp.com/ecmdocs/ECMP1196986/html/GUID-76CEE44B-CBC2-45C0-917D-1B7C43576933.html