To the best of my knowledge the CAAV still requires minimum 500 on type to issue a conversion from a foreign licence. And they are very specific about it, i.e. they require actual A321 time for Vietnam Airlines foreign pilot conversions, they don't count A320 or A319.
Vietjet isn't short of pilot applications, a very large number of hugely experienced local Vietnamese pilots from Vietnam Airlines have applied for the job.
I would be very very very very cautious about paying money up front to anybody for a job with Vietjet. Especially an agency that nobody's ever heard of.