Bringing 'Atta' concept to Buddha's teachings
It is possible to bend the Buddha's message (if you so wish to do) because the Buddha never denied Atta in an Essential sense, he only pointed out that within empirical experience (all the way up to the perception of cessation) no 'thing' can be said to be constant and unchanging, as a self would be required to be.. hence the Mulapariyaya Sutta.

Whilst the Buddha was very clear with regards to the lack of evidence for Atta within the empirical world, the Brahmajala and Potthapada Suttas shows that with regards to the Transcendental Atta (which is the Atta that most darshanas went for - Brahman/Atta is usually seen as beyond experience, commonly stated as 'neti neti' - 'not this, not that'), he asked people to avoid speculation (because whatever that 'transcendental' is inferred to be, it cannot be perceived and therefore cannot be verified)

The Anatta doctorine is very subtle, a not insignificant number of schools of Buddhism have gone towards either essentialism (brahmanism) or annihalationism (nihilism) at some point. Yogachara has the nature of Parinispanna, which is a transcendental Atta. Mahayana developed the Tathagatagharba, which makes the Buddha a kind of Atta for Existence. The Buddha would have likely not concurred with these though!