TG-
The word "voluntary" is not mutually exclusive with "highly paid."
I assume JKM is accurate in his description of Shaw as "highly paid." The CIA has never retracted, corrected or clarified that description of Shaw by their own historian.
As a non-CIA officer, Shaw was likely not instructed or ordered anywhere, but was likely asked to perform certain tasks, and voluntarily did so, and then was highly paid.
Shaw may have contributed large amounts of information to the CIA, though verbally, or may have performed tasks for which there is no revealing paperwork, such as moving goods internationally through front companies.
Shaw may have been a source for documents written by others, including CIA officers.
My take is Shaw was among a group of US assets somewhat monitoring LHO, and other Cuban assets, in New Orleans, and for good reason. LHO was a declared Marxist, had been to Russia, and may have been seen in company of G2'ers or DGI'ers.