US with good food surplus/schooling/more mechanically inclined recruits/etc easier to 'train' than SVN/etc ...?
Yes, however country people have their advantages too. Used to hard work, usually in good form, accustomed to hard conditions, possessed of a wide variety of common skills. That was as true of the Vietnamese troops as it was of the US. And like US troops, Vietnamese draftees brought in a varying degrees of education. Usually about the 5th grade for Vietnamese peasants. Ethnic Cambodians, Cham, and Montagnards were generally illiterate in their own language, and not highly skilled in Vietnamese. Ergo a Vietnamese willingness to accept the CIDG program under US direction.
North Vietnam had a similar advantage over the South. It was far more culturally and educationally homogeneous, had a larger population, and was maintaining an expeditionary force effort that did not require the defense of their home area against anything other than american bombs.