My initial thoughts would be is the bike suitable for the roads in Vietnam, having said that people have ridden around the world on CBR 250 road bikes.
Bikes like CRF250L or Suzuki DRZ400 are more suitable for roads in Vietnam, especially when you go on a long-distance tour and wanna try some off-road tracks. If you want to ride your own bike to Vietnam, you need to have an approval letter from the Vietnamese Ministry of Transport. You can read more info at: Vietnam Caravan Tours – Crossing borders with your bike
The fee is around 600-700USD/ bike.
Thanks for the heads up, lots of Thailand based riders would like to travel through Laos to Vietnam, any information you can offer would be very useful.