Saw a scoop.it post that said the brightness of the EVF and OVF can be set independently using QMenu / "LCD brightness".
What I am seeing is LCD Brightness can be set independently for the EVF and LCD. If you have your eye to the viewfinder, "LCD brightness" adjusts the EVF.
However it does not appear to affect the OVF HUD. The HUD seems to gain up/down on it's own depending on the available light.