Oooops. I misread your post. So there is a UA desk at Shanghai and Vietnam.
Never mind on my previous post. Derp on me.
Well I may have misspoke anyway - I see pictures of UA airplanes at Hanoi intl but I can’t find a map or pictures where they have dedicated ticketing stations there. It may be they only have codeshare flights with VA or another airline. The pic associated with Vietnam was only a runway so could be they only did a refueling stop etc.