Those Nungs were damned good fighters

From Once a Warrior King by David Donovan.  

For some reason CIDG units were often made up of men who were not ethnic Vietnamese. In the Delta the CIDGs were usually Nungs, men of Chinese ethnic background but who were Vietnamese by nationality. Many of these men were recruited from Cholon, the Chinese sector of Saigon, and had little in common with the rural Vietnamese. This social dichotomy was always a problem, but I was willing to put up with it because those Nungs were damned good fighters. They had good leadership from the A team and they had good morale, a quality painfully lacking in the regular Vietnamese forces.

The CIDG units had good morale because they liked working for the Americans; they were highly paid and well supplied. But they knew that if their job performance was not up to par they could be fired, and if they were fired from the CIDG, they became eligible for the Vietnamese draft. The draft would doubtlessly put them in the Vietnamese army, where they would have to do the same fighting for less pay, under worse living conditions, and without the direct American assistance. In short, the Nungs did their jobs well because they knew when they were well off.