i'm a vietnamese, i live in hanoi in hanoi, it seems like there are are 2 main theravada groups they participated in the same places but thay have sub groups or somethings 1 the people practice under vien minh bikhhu
Theravada exists in South VN from monks going to Thailand and Shrilanka. Most of VN is Mahayana from under the influence of China. You can see this documentary clip - http://www.youtube.com/watch?v=FjvGopI52_M