I want to clarify that most of the work of these groups is in Burma. Often, when people refer to inside Burma, they mean central Burma, as opposed to the ethnic states, but a lot of groups will have offices both in the ethnic states of Burma and Thailand as a fallback position. They're actually working in the ethnic states.
In Burma you have a situation where the government control does not actually cover the entire country. There are large parts of the country with mixed administration, where you have ethnic governments that exert as much or more control than the government. You can operate effectively in those areas without any government approval, but of course, if the government military comes into the area, you then become a target.