Due Diligence and Ongoing Monitoring

Do you classify this type of service provider as a "vendor"?  I am getting conflicting information on whether they should/would be considered a vendor.

Hopefully this excerpt from the Interagency Guidance answers your question:

"A third-party relationship may exist despite a lack of a contract or remuneration. Third-party relationships can include, but are not limited to, outsourced services, use of independent consultants, referral arrangements, merchant payment processing services, services provided by affiliates and subsidiaries, and joint ventures."  (page 30)

We consider them out of scope vendor, and we don't conduct a due diligence.

Is this correct? should we do our due diligence? What do we ask/request?