There's the idea that everything is defined in relation to something else, except the Dao, which is itself. As a corollary, anything you can name, i.e. define, isn't the Dao. In the ddj it's not said explicitly like this but it's something that can be pieced together from various chapters.

Might you need both? From what I've seen, dig deep enough in a particular hole, be it theoretical physics, statements about God, etc. and you get the paradox that two different things imply each other mutually. You can't have one without the concept of none, and you can't have none without the concept of one. See Godel's incompleteness theorem, the particle vs. wave situation, etc.

Are you saying that this concept is mostly absent from the Taoist texts you've read?