I dont think so!
Hi Nigel, you just need a visa, not necessarily an approval letter. Here's a link to find out more:
Hi... Only prior visa approval is required... Visa is availed on arrival at any Vietnam airport
The emigration process was smooth, no problem faced there. Just fill the forms available at the emigration counter and submit it with the required documents and fee. After few minutes of waiting you'll receive the visa impounded on you passport. Its quite simple and easy process.