Probably not, Matthew Amster-Burton at Gourmet.com concludes. After noticing the country's penchant for sweetened iced coffee and blended fruit shakes, he had wondered if the Vietnamese weren't the first to make the Frappuccino. His theory is soon disproved—since blenders have only recently become available to the masses in Vietnam, he learns, they couldn't have invented the blended coffee drink.
Still, it seems like he's onto something: after sending his own Vietnamese iced coffee for a whirl in the blender, he's plenty happy with his own Vietnamese-style Frappuccino. Even if it's not quite traditional.