I assume you want the "6-bit encoding", which is specifically tailored to each Leica lens and any "corrections" are only applied when you shoot JPEG and not in RAW. (Leica also says it corrects "cyan vignetting" WHEN you use the IR-cut filter: http://leica.nemeng.com/004f.shtml
Since the encoding cannot and does not communicate shooting aperture to the camera, light fall-off is not corrected. CA also depends on shooting aperture and I seriously doubt it is corrected either. Both parameters are specific to each Leica lens and obviously they are not the same with Japanese lenses.
There have been suggestions that the camera "estimates" the shooting aperture with the encoding. If that's the case, any correction is an also an estimate and can actually be worse than no correction, especially with Japanese lenses.
I strongly believe that providing the focal length to the EXIF is the only real benefit of the encoding, the lack of which has never impaired M-shooters. Alex Shishin (photo.net) is one of those who encountered no problems with un-coded lenses on the M8.
You need nothing more than the usual LTM-M adapter -- 50 for the Nokton. Since the M8 doesn't have framelines for the 15mm, any good adapter will do.