Is there a concept in Wicca/neo-paganism like this?

The concept of Brahman in Hindu Dharma???
A concept of a very high power that is behind everything, like the Tao in a sense???
Serious answer please...

Yes. To some Pagans, there is One Source and all gods and goddess' are merely aspects of that Source.

Wicca is one religion and Noe-paganism is many many religions so yes there is probably some people that are Noe-pagan that believe this

Yes. Wiccans call it the All. Some Wiccans are monotheistic and this is their only God, but they believe God encompasses many different aspects. Wiccans are allowed to develop their own ideas about God so long as they are what you truly feel.

There are so many types of pagans and some do have that concept. Not all pagans are strictly polytheistic. Especially those who follow shamanistic paths have a belief in a Great Spirit or entity of that nature. Pagan faiths encompass nearly every understanding of God.

Yes and no. Traditionally, the God and Goddess of Wicca are nothing like the Hindu concept of Brahman, but Wicca has a very loose theological structure, and so long as the individual sees that "All" being/deity/power as dual and complementary and embodying masculine and feminine energies equally, it still fits within the boundaries of Wicca. Paganism is much broader and does not describe one particular religion but a multitude of religions, and there are definitely some Pagans who see deity in this light.
Venus Bless