It's half a 16 spoke wheel. You could do 1X, you might even get closer to tangential with 2X if the PCD is a very small fraction of the ERD. On the other hand, why would you? If you wanted that side to apply torque, you wouldn't have half the spokes missing 🙂
Is there any reason why the 8 spoked side would have to be laced radial?
Depends on the hub. If it has standard spoke flanges, then no. My only triplet build so far used a Tune Mag150 hub, and the NDS has to be laced radially with that hub.
Is there any reason why the 8 spoked side would have to be laced radial?