I think there are lots of non native speakers filling that void. Schools offering a joke salary are also willing to lie to the parents about the nationality of the teacher. I don't want to stereo type all people teaching in China who don't come from Canada, The US, Australia, NZ, SA, and the UK. In fact a lot of them actually work pretty hard because it is so hard for them to get hired, based on accent or skin color. Where as their counter parts from English speaking countries can often be entitled little vacation teachers.

It all depends on each individual case, there are a lot of good teachers out there. But yea if you are wondering who is taking those jobs that keep popping up for less than enough to live on for slave hours a week it is those people.