Question re towplane airworthiness (USA)

I am posting the following for my local glider operation:

"Our Pawnee has two airworthiness certificates, one for normal flying
and one, restricted, for towing. When towing it is operated with
specific limitations spelled out on an operators handbook supplement.
Our tow pilot believes that our Scout should also have a second
airworthiness certificate for towing and refuses to tow with it until it
does. I need to find another operation that tows with a Scout and get
their take on it before I approach the FAA for a finding. My take on it
is that it left the factory with a provision for a tow hook so the
standard airworthiness certificate covers it."

Anyone have an answer to this?