5D III RAW file (in sRAW size) was easily imported by Lightroom 4 and I didn't noticed any incompatibilities.
you are likely seeing the jpeg embedded in the raw file, LR4 cannot open raw yet.
However, Adobe has both a beta Camera Raw and a beta dng that will let you convert them to view and edit in lightroom. go to the Adobe labs site and get the betas. We will probably see a beta lr4 soon.