The processes are essentially the same, but D-Nice's slides have a somewhat different purpose.
The phosphors in a plasma TV are generally more susceptible to change during the first 100-150+ hours of use. So the similarities between D-Nice's prep and the break-in process you see some people follow, is that you run a specific order of colored slides to evenly/uniformly age all of the phosphors when they're more susceptible to change. D-Nice also does it so that others can age their panels the same way he aged his reference panel for optimal results when you plug his settings in. Because as you may know, plugging in calibration settings is rarely perfect due to panel to panel variations.
Now the whole 'break in' procedure is still up for debate. Some people feel that it is essential to run the slides during the first 100-150hrs of use, as it reduces or eliminates the chances of Image Retention etc., but I'm personally on the side of thinking that it's just BS. Resistance to IR varies from panel to panel, model to model. IMHO, there's nothing that you can do to reduce the chances of IR, outside of keeping the contrast lower and mixing up your viewing content a little, avoiding stationary logos for long periods of time. There have been so many cases of people not running the slides and have no IR issues whatsoever (like myself), and others running the slides and getting IR, or even burn in problems.
I do feel that there is some benefit in running the slides, even if you're not using D-Nice's settings, to evenly age the phosphors. But personally, during the first 100-150hrs of use, I would just avoid black bars as much as possible. Not worth the time IMO.