Hmm, how likely is a Vietnamese intervention?
Propably unlikely because the Thais would have to be much more dangerous than they are in order to have Cambodia calling in the Viet, is it possible for Cambodia to use the threat of "make peace or we call in Vietnam!" as a bargaining chip?
If the Thai already struggle with the Cambodian army, the Vietnamese army would rip them a new one...
China would back Thailand over Vietnam, I imagine.
The Chinese have given the Thais the license production for the WS series of long range rockets.