Nhat Hanh's approach has been to combine a variety of traditional Zen teachings with insights from other Mahayana Buddhist traditions, methods from Theravada Buddhism, and ideas from Western psychology—to offer a modern light on meditation practice. Hanh's presentation of the Prajñāpāramitā in terms of "interbeing" has doctrinal antecedents in the Huayan school of thought, which "is often said to provide a philosophical foundation" for Zen.
Source: The Making of Buddhist Modernism (2008)
Vietnamese Buddhism in general is very eclectic, with many followers of Pure Land, Zen, Tiantai and Theravada traditions. In the 13th century Vietnamese Zen was somewhat fused with Confucianism and Taoism, but by the 18th century Zen returned to its roots with the founding of the Liễu Quán school. That being said, I think it's safe to say Thich Nhat Hanh is quite admirably doing his own thing.