Yes of course it should be 99. However the most important you have to be very clear the Labor Law & specific requirements in your customer and payroll schema (Time schema as well if any).
Some specific requirements in Labor Law in Vietnam are: Social Security, and esp PIT Personal Income Tax. They are given by Vietnam government so take time to communicate with HR in Vietnam to clear it. I have done it before and it's so complicated (even I am from Vietnam as well) 
but it's great chance for you to very clear payroll schema.
btw if you want to use new country grouping: I have some documents for u:
Copy wage type between country groupings
Maintain Processing, Evaluation and Cumulation Classes
If you want to have more documents involving Schema, plz check in my blog: Useful documents for Schema & PCR configuration
Regards,
Woody