My experience with Hmong is that they did not become Christians until they got to America or shortly before.
http://www.hmongcenter.org/tradhmonrel.html
http://news.minnesota.publicradio.org/features/200108/27_goetzk_shaman/sidebar.shtml
What I did quote was from books. Since you have had first hand experience, I will bow to your superior knowledge on the Hmongs conversion to Christianity.