Hi,
I'd like to share our Zendesk Guide page for our external collaborator. I know only view rights could be set by changing "Visible to" setting for the end-user organization which belongs in the collaborator's group. On the other hand, There are no way to give create/Edit/Delete authentication for them without any leak our information in Zendesk support page(Customer,Organization, and explore clickable on left panel of Zendesk support UI), according to your operator's responding on #10423759.
I hope it to be better in the future.
Thank you,