Short answer — no. In Vietnam, motorbikes with an engine up to 50cc fall into a category that does not require a driving licence. That's exactly why 50cc bikes are so popular with tourists and long-stayers: hop on and go, no licence paperwork.
Traffic police (CSGT) do not fine you for riding a 50cc bike without a licence — it's legal. But some things are checked for everyone, regardless of engine size:
"50cc, no licence" only works if the bike is genuinely 50cc on the documents and the papers are clean. If the papers say a larger engine or the bike has a shady history, the benefit disappears. That's why we sell only bikes checked against the police database, with a full set of documents.