The distance from the rear element of the Olympus 17mm lens is fairly close to the sensor. Unless there is a lot of non-uniformity correction going on within the camera to correct for fall-off at the edges, I have a hard time believing that a Leica wide-angle lens will be any worse.
The Kodak sensors used in the M8 and M9 use offset microlenses to correct some of the problems with light fall-off at the edges with wide-angle lenses with rear optics close to the sensor. 6-Bit coding for wide-angle lenses also brings in a non-uniformity correction to prevent light fall-off.
I use a Nikkor 24mm F2.8 on my M8, with an F-Mount to M-Mount adapter.
A retro-focus wide-angle lens does not have these problems.
