Any question answered...

I don't think you can do that with Omniums (or any other GXP crank/BB), because the NDS crank will hit the bearing as you tighten it onto the axle and create excessive preload.

Depends on how many shims you've got between the BB shell and the cups, obviously. You might be able to move things around a bit by shimming one side in preference to the other.

For what it's worth, I seem to think that the SRAM GXP single speed cranks may have a slightly different chainline, which might work a little better with the Goldtecs.