It could work at some / low to medium level
Generally up to B1, however there are good ones who can do B2.
With language teaching, it isn't so much your command of the languages as your ability to teach, plan lessons, follow a syllabus and prepare people for exams.
a native speaker cannot be replaced.
One issue is that there aren't always enough to go around who have the right skill set and sometimes the best candidate for the job is someone who has made the same journey as the learners.
I'm hiring now, two posts. For one of the posts, the best candidate is a Pole. He's lived in the U.K., is well qualified and has good teaching experience. Incidentally, in terms of salary (very high) and terms (rotational in Africa, direct hire, public sector) the job is probably in the top 5% or less of EFL posts worldwide. I didn't advertise it since the last time I did, there were around 600 replies of which about 550 didn't match the basic requirements mentioned in the ad and of the remaining 50, around half were known to me and had a poor reputation and the others had either the wrong type of experience or other warning bells rang. So I asked a trusted source for a recommendation.
Sadly, he's currently blowing a bit hot and cold since he doesn't quite believe it and thinks it's too good to be true!
Incidentally some universities too have Poles, Czechs and Italians lecturing in their English Departments.