Are there any exceptions with this type of visa?

Yes, Vietnam visa on arrival is NOT VALID for OVERLAND ENTRY. The three international airports in Vietnam that you can receive your visa stamp with this approval letter are: Noi Bai International Airport (Hanoi), Tan Son Nhat International Airport (Ho Chi Minh City) and Danang Airport (Da Nang).

Note: If you plan to enter Vietnam by land or cruise, please visit a Vietnamese embassy to get your visa.