On the topic of Thai classroom assistants and are they useful to a foreign teacher? I have six teachers with me. (One for each level that I teach.) They are all different and they all need to be treated differently. One of them watches my lessons attentively and is up like a shot to help me through something if she thinks my class doesn't get it. We work well together as a team. Another teacher considers this another 'free' period and doesn't ever even show up! The remaining four have levels of involvement in between these two extremes!
I work well with all of them and don't have any problems at all. The reason is that I work with what they give me. If they want to get involved then they can and if they want to slope off and hide, then that's fine too. Farang teachers usually create their own problems with other teachers. Often they don't see how bloody annoying they are! They stumble through their relationships with other members of staff because they don't think that other staff members are important. Or they think that they know better in the classroom and eagerly embrace every opportunity to prove it.
Occasionally there may be genuine cases of personality conflicts, but I've never seen one where the Thai teacher was the one being a dick. The point is that Thai teachers are what they are. They vary wildly in terms of ability and commitment. You learn to work with the tools in the toolbox.