Wikipedia says, about Vietnam:
Followers in Vietnam practice differing traditions without any problem or sense of contradiction. Few Vietnamese Buddhists would identify themselves as a particular kind of Buddhism, as a Christian might identify him or herself by a denomination, for example.
... and goes on describe aspects of Vietnamese Buddhist practice.
It also says:
The overall doctrinal position of Vietnamese Buddhism is the inclusive system of Tiantai, with the higher metaphysics informed by the Huayan school (Vietnamese: Hoa Nghiêm); however, the orientation of Vietnamese Buddhism is syncretic without making such distinctions. Therefore, modern practice of Vietnamese Buddhism can be very eclectic, including elements from Thiền (Chan Buddhism), Thiên Thai (Tiantai), Tịnh độ Pure Land Buddhism, and popular practices from Vajrayana.
The central and southern part of present-day Vietnam were originally inhabited by the Chams and the Khmer people, respectively, who followed both a syncretic Śaiva-Mahayana (see History of Buddhism in Cambodia) and Theravada Buddhism.
And about Cambodia:
Theravada Buddhism is the state religion of Cambodia, which has had been presented since at least the 5th century.
Tu Vien Hong Duc is described as:
While Tu Vien Hong Duc is therefore best classified as a Pure Land Buddhist temple, it is much more a Vietnamese Buddhist temple.
According to Google Maps, Phuoc Vien and Tu Vien Hong Duc are located in the same building.