Nirvana is described in Samyutta Nikaya 43 as "the unfabricated (unborn?), the uninclined, the truth, the far shore, the subtle, the very difficult to see, the unaging (eternal?), the stable, the unintegrating, the unmanifest, the unproliferated (nippapancan), the peaceful, the deathless, the sublime, the auspicious, the secure, the destruction of craving, the wonderful, the amazing, the unailing, the unailing state, Nibbana, the unafflicted, dispassion, purity, freedom, the unadhesive, the island, the shelter, the asylum, the refuge, the destination."
Also from another source in Buddhism Stack Exchange, I see Samyutta Nikaya 43 as quoting Buddha as saying "There is, monks, that base where there is neither earth, nor water, nor heat, nor air; neither the base of the infinity of space, nor the base of the infinity of consciousness, nor the base of nothingness, nor the base of neither-perception-nor-non-perception; neither this world nor another world; neither sun nor moon. Here, monks, I say there is no coming, no going, no standing still; no passing away and no being reborn. It is not established, not moving, without support. Just this is the end of suffering."
The Tao Te Ching chapter 1 says "The tao that can be told is not the eternal Tao. The name that can be named is not the eternal Name." while chapter 7 says, "The Tao is infinite, eternal. Why is it eternal? It was never born; thus it can never die." And chapter 14 says, "Look, and it can't be seen. Listen, and it can't be heard. Reach, and it can't be grasped. Above, it isn't bright. Below, it isn't dark. Seamless, unnamable, it returns to the realm of nothing. Form that includes all forms, image without an image, subtle, beyond all conception. Approach it and there is no beginning; follow it and there is no end. You can't know it, but you can be it ..."
The Bhagavad Gita states in chapter 2, "The Atma is neither born nor does it die at any time, nor having been it will cease to exist again. It is unborn, eternal, permanent, and primeval. The Atma is not destroyed when the body is destroyed.", "This Atma cannot be cut, burned, wetted, or dried up. It is eternal, all pervading, unchanging, immovable, and primeval. The Atma is said to be unmanifest, unthinkable, and unchanging." And in 12.3, "... the imperishable, the undefinable, the unmanifest, the omnipresent, the unthinkable, the unchanging, the immovable, and the eternal Brahman;". In addition, other texts use "neti neti" (not this, not this) to say that Brahman is indescribable or all that is not impermanent.
From the above, it looks like all are the same, yet if we look at other references, Tao and Brahman is the origin or source of all things, but Nirvana is not. And Brahman can also assume attributes in the changing world or become God the Person or Consciousness, but Nirvana does not. Also, the aspirant can become or become one with the Tao or Brahman, but in Buddhism, one has to "unbecome" or let go of all that is impermanent, to realize Nirvana. But then again, Tao and Hindu sources also discuss letting go of all that is impermanent.
My question is, do Buddhists ever consider that it is possible that goals in other religions like Tao and Brahman, may in fact be the same as Nirvana, if we look beyond the semantics. And therefore, the practices in these religions, may in fact lead in the right direction?
Of course, we can also say that one could start off as a Taoist or Hindu, but after a few Jhanas, move towards being Buddhist, towards Nirvana. Or perhaps, all these labels are irrelevant at that point.