No. There is likely no chance any US, South Vietnamese, or even Allied forces would have ever encountered Chinese troops during the Vietnam War.

Between June 1965 and March 1968, approximately 320,000 Chinese soldiers were stationed in North Vietnam, with troop numbers peaking in 1967 at about 170,000. The vast majority of these troops served as technical advisors, but certain units were assigned to assist with and man North Vietnamese anti-aircraft batteries. They would not have been assigned to combat units headed south or across the border into Laos or Cambodia.

I recommend Qiang Zhai's China and the Vietnam wars, 1950–1975 for further reading on this subject.