Errm, as far as Xorg is concerned, it only communicates via sockets, not depending on a certain type of them. While there is a convention/standard for transmission via TCP, communicating via Unix Domain Sockets instead is equally common (and *might* slightly reduce overhead). Unix Domain Sockets do not built on the IP layer (as TCP sockets do), thus are not IP addressed. They use filesystem namespace addressing instead (or non at all and do file descriptor sharing among processes). There's a convention to prefix the sockets with the "/tmp/X11-unix/" path. See socket(7), unix(7). Note that these sockets are not the same as FIFOs aka named pipes.
Without further configuration, Xorg handles both TCP and Unix Domain Sockets.