I will not be of much help but here is what I was able to find.
Translated version of http://www.dai.vn.ua/podrozdil.htm
Go to the DEPARTMENT LETTER GA MIA to foreign nationals, section. I will give you some basic knowledge.
also
Driving a Car in Ukraine
Here is a link from the embassy in Vietnam
Embassy of Ukraine in the Socialist Republic of Vietnam - Publications
I suggest you call them (the Vietnam embassy) and ask them if your passport would be valid. I dont think you should have a problem.
From what i understood, you need an international drivers licence