The Lolo speak a Sino-Tibetan language.  Specifically, it is in the Tibeto-Burman group of the language family.   Their language is a completely different language group from Vietnamese, which is of the Mon-Khmer group.  

It is said to be closely related to Burmese, linguistically, though the language has yet to be thoroughly studied.

It has been classified as follows:  Sino-Tibetan, Tibeto-Burman, Burmese-Lolo, Lolo, Northern, Yi, Unclassified Dialects

     Two researchers from the University of Texas at Arlington  (Dr. Jerold A. Edmondson and Dr. Kenneth J. Gregorson) did some research into the language of a Lolo speaker in  Yen Minh District, Ha Giang Province  This language proved to be an  example of Yi (Lolo), which is spoken by 7 million people in China, though with considerable variation from place to place.  They said that the language possesses "six tones, tense/lax voice quality and many uvular consonant  initials. . . . {as well as} the  trademark set of stop contrasts, having four manners of articulation, e.g.,/p  ph b mb/."  There is some uncertainty concerning the Ropal code for the Lolo language.  It may fit under the SIL code: MUS, which stands for the Musi language.  Musi is a vernacular of Yi which is spoken by at least some Lolo in Vietnam.  Very likely it is the same as investigated by Gregorson and Edmondson.