It shouldn’t be surprising if there are similarities between Taoism and Mahayana Buddhism.
These similarities helped to facilitate the acceptance of Buddhism in China. Also, Cha’an (Zen) specifically has often been described as an amalgam of Buddhist and Taoism influences.
The concept of the Dharmakaya, however, isn’t original to Chinese Buddhism. The Eternal Buddha of the Lotus Sutra is an example of the Dharmakaya. According to the Lotus Sutra, all buddhas are embodiments of the Eternal Buddha.
Several different sects and schools of Mahayana Buddhism explicitly teach that Dharmakaya is more or less synonymous with the Buddha-nature in all things and beings. I’ve never seen a Mahayana school or sect which rejected this teaching:
In his Notes on ‘Essentials of Faith Alone’, Shinran, in commenting on a hymn from Shan-tao, makes the following observations about Nirvana[20]:
“Nirvana has innumerable names. It is impossible to give them in detail; We will list only a few. Nirvana is called extinction of passions, the uncreated, peaceful happiness, eternal bliss, true reality, Dharmakaya, dharma-nature, suchness, oneness and Buddha-nature. Buddha-nature is none other than Tathagata. This Tathagata pervades the countless worlds; it fills the hearts and minds of the ocean of all beings. Thus, plants, trees and land all attain Buddhahood. Since it is with these hearts and minds of all sentient beings that they entrust themselves to the Vow of the dharma-body as compassionate means, this shinjin is none other than Buddha-nature. This Buddha-nature is dharma-nature. Dharma-nature is the Dharmakaya.”
Muryoko: Journal of Shin Buddhism]Muryoko: Journal of Shin Buddhism
The Dharma body is the same as the intrinsic, pure Buddha nature that resides in all things everywhere. The deluded self can find peace when it understands that it inherently possesses Buddha nature, that this nature pervades all things. Our wish to find what is real and permanent can only be resolved by attaining the Dharma body.
Hsingyun.org]Hsingyun.org
Despite the names and forms given to the dharmakaya Buddha in Tibetan Buddhism, the dharmakaya is an abstract concept - it is the primordial truth that is beyond form, space and understanding, where all beings are united and phenomena unmanifested. It is the unchanging, eternal absolute, where everything is united in Buddha nature…
The dharmakaya is also identified with Buddha nature, where there is no distinction between the Buddhas and everyone else. Buddha nature is a Mahayana belief that everyone is already a Buddha, and that Buddhahood is not something to be achieved, but to be revealed or uncovered by clearing away our ignorance and confusion with the practice of wisdom and compassion as guided by the Dharma.
http://pemanorbuvihara.my/buddhism/buddha.html]http://pemanorbuvihara.my/buddhism/buddha.html