I asked Sheldon about this issue, and he responded with what I expected him to say (but he'd not said directly in his wheelbuilding article):
Originally Posted by Sheldon Brown
There's no problem with this, because the tension is very low on the left side of a derailer type rear wheel.
Anyway, I think I'm going to go ahead and build up that 7-speed freehub with radial non-drive-side spoking. And a 480g single-wall welded-seam Araya 27" NOS rim. And butted spokes.