I've never had any problem to let another guy (a local, more to the point) share my hotel room with me in Vietnam. Isn't it much like in Laos, that what they're really trying to prevent is foreigners staying with local ladies they aren't married to? I've never had the impression that these restrictions are enforced as far as gays are concerned, in both countries.

The only thing I've been cautioned about is that I shouldn't stay with a Vietnamese at their house or apartment, because they're supposed to register you with the police, most likely don't know the procedure and then might end up getting into trouble. I've declined a number of invitations because of this, but I prefer staying at a hotel anyway.