Essentially yes. Here's how you get a graphical session on a remote machine: export your local /dev/draw, /dev/mouse, etc. via 9P to the remote machine, then run the GUI on that remote machine. It'll write to /dev/draw, read from /dev/mouse, and so on with no idea that all those file operations are actually traversing the network.
Thinking about it a bit more, indeed. Unless you compress the data of course, which could theoretically be done transparently by the graphical session that owns the framebuffer device.
But I think that /dev/draw (as the name implies) was likely a drawing API? A bit like X11, when the only thing GUI apps did was to draw primitives like circles, lines, text...
