It's very important when it's an actual communication course, which requires a speaking and listening component. The teachers who do this course must be able to teach in English, they can't just write everything on the board. The engineers who do this course must be able to speak as they will converse with native speakers in their jobs.Knowing only the grammatical part of English won't save you when someone yells"look out".
If it's just a normal language centre program then that's a different story, I was referring to communication courses that are held.
Thanks for clarifying. You are absolutely correct. We were discussing entirely different training situations. Thankfully, Vietnam never got as deep into the situation as some other countries.