How integral is the synergetic aspect of buddhism?

I remember reading, in the 1st book I picked up on Buddhism, that it was a synergetic religion, literally, that it combines with (I suppose indigenous) traditions, such as the tao, and bon. Did the Buddha ever talk about this aspect of (what has ended up as) his teachings? Are there any interesting studies or way of thinking about Buddhism in those terms, general to all that it has taken up and made its own?