"maybe with the Montagnard tribes"
Khmer Mountain Tribes' Flag
Creative Commons Attribution Share AlikeKhmer Mountain Tribes' Flag - Credit: http://commons.wikimedia.org/wiki/User:Froztbyte

This term refers to the "mountain people" of Vietnam.  These people lived in the Central Highlands and were considered America's most loyal allies in Vietnam.  Other Vietnamese considered them to be "moi" or savages.  They were largely Christianized.

They helped America in the war in numerous ways, especially by housing troops.  Up to half of the Montagnard tribes were killed fighting alongside American troops.