As to Thich Nhat Hanh, it has been awhile since I read his works, but to my recollection largely he focused on similarities in ethics and spiritual practice, not claims of unity or similarity in metaphysics. Is prayer similar to mediation? Sure, but it depends on the tradition, because both are so varied. Do the major religions teach similar ethical precepts? Absolutely. That doesn't make them the same religion, or even similar religions.
The Buddha is said to have lived on a single grain of rice a day. Christ lived in poverty, associated with the outcasts of society, and suffered a grisly death. These aren't guys who are going to give you a car, or a nice house.