in terms of image quality alone are they the same??
In most situations I suspect you would have a hard time seeing any difference at all, but at very high ISOs the 6D's images look a bit less noisy (or, one might prefer to say, the quality of noise on the 6D is superior), and if you have or want to push shadows a lot, the 6D generates considerably less noise and banding than the 5DIII.
I usually find DR discussions - esp. in the endless Canon vs Nikon debates - tiresome, especially because the differences between the two groups of sensors strike me as being considerably overstated. I still do, but I'll note that a week ago the other half (armed with a 6D) and I (armed with a 5DIII) were taking photos at a vintage car show outdoors in the middle of a brilliantly sunny day, i.e. lighting conditions most of us would ordinarily avoid given the choice. We had no choice (other than not take photos at all), and the circumstances were all wrong for setting up tripods for multiple exposures (we were just taking casual photos for fun and tripods would have been inconsiderate of others). Unsurprisingly, lots of shadows, including the grass under the cars, came out more-or-less black. Processing the files in LR, it was easier to bring out clean shadow detail from the 6D's files than from the 5DIII's. That said, the differences were only really noticeable via pixel-peeping - even viewed on a 30" monitor you would have to look for the noise/banding on the 5DIII's images to notice it; but they're there nevertheless.
If those differences matter to you, then yes, the 6D, in those regards at least, makes better images.