PTEX is yes. But it can be incorporated into Mari, C4d, Renderman, Houdini and Mudbox etc....it does need to be compiled.

We are currently looking at it for the future but have to wait and see. From what I know though it doesnt render in Mental Ray (would you believe LOL)

Again back to Zbrush....you can paint a model without uvs, and then just generate them in zbrush after...they work fine

Jay