Is the native PO field (otherrefnum) required for Purchase Orders in Netsuite or is it ok to create a custom field?

That field is used on SOs and is a reference to the customer’s PO number. It’s not required by default.

yea that's how we currently use it but I was building out a management tool using a custom field so it allows them to change the PO# without touching the underlying record. However one thing i noticed is that when you are searching the Sales order or invoice # it also shows whatever is in the native PO# field. Now I am thinking of having a workflow/script writeback to the underlying record so at least it's handle programmatically and not through the UI to make our external audit team happy.