While there was always that one rumor going around the barracks of a lone American defector who was now fighting for the VC, there is simply no proof that a white westerner ever fought on the side of the Viet Minh or the VC/PAVN.

The North Vietnamese fought a war very much revolving around the ideas of combining politics and warfare, something which was really taken advantage of during the Vietnam War. While the North was fighting in the south during the war, they were also fighting a worldwide war for political support. The image of a western man fighting for the FNL or wearing the PAVN uniform would have been a striking one and would definitely been an important part of Vietnamese propaganda aimed at the US and their allies in the war.

So, in the end, there is no proof or evidence of a western man (i.e. American or French) who actively fought under the banner of North Vietnam.