You don’t need any kind of viewfinder, be it O or E, to focus an APS-C camera with a 12mm lens at f/22.
The hyperfocal distance is somewhere around 50cm, and something like 30cm to infinity will be in focus.
You are presumably using f/22 for really deep DoF, and not just to slow down, so why not use the hyperfocal distance, instead of running the risk of focusing further away than 50cm and thus ruining your foreground DoF?
And with ND10 and f/22 you really would be very unlikely to use the viewfinder anyway, as long as your camera has liveview.