While not as convenient as making the text color in LO transparent, you can do it in SketchUp. Then create a scene…call it Watermark, or Draft or whatever:
Then in LO, add that scene on top of your viewport(s). Also if you know you’re going to use drafts a lot down the road, perhaps it’s better to make the Draft text in it’s own SU file…save that somewhere safe where it won’t be moved…then create your own template. That way you never have to make it again. And if you ever want to change the font or color, it’s as easy as making the change in that Watermark SU file.