The Epson PhotoRAW devignetting feature works until a certain level. If you do not apply many other tweaks like AE correction, contrast curves, unsharp masking, color filters and so on, the noise produced by the antivignetting algorithm is acceptable. But if added to a lot of other tweaks, it makes the pictures useless.
The Summicron 28 vignets like the Color Skopar 28, I have no knowledge about other Leica wides concerning this issue. Afaik, the Zeiss 15, 18 and 21mm wides do also vignet, but significantly less than the CV ones (especially if used on film). Alas, on the Epson, I fear almost any wide will produce a certain amount of vignetting dued to the sensor design.
Didier