jsfboat you won't get a simple answer to that here, for the simple reason that none of the medical regulations are written in English and none of the CAAV doctors speak English. A few things like BMI<30 are well known, but the rest they seem to make up on the spot
They have failed guys recently for missing teeth, "polyps in the sinuses" that were completely undetectable by western specialists, etc.
And no, you can't do the medical beforehand, you have to actually arrive in VN to start your new job and THEN get sent for the medical
If you're unemployed, then nothing to lose, but it would be very very very very unwise to quit a secure job and come here with a known medical issue, on the hope you'll get through
Also there's no B737s here in Vietnam, you know that right?