Excellent name Marc but you're spelling it wrong!
DMT plates wear out over time as the diamonds come off the plates. I don't think they grind away but I could be wrong. My experience has been they last as long or longer than the stones unless you are using them to flatten stones and then they wear more quickly.
Yep that would work just fine. Many people poo poo using the diamond plates for sharpening and I'm not sure why besides the fact that they're really fast and have very unpleasurable feedback. They work quite well especially on super hard steels that are difficult to sharpen on regular stones.
Check out the Atomas. They're really nice to sharpen on. The mesh gives you better feedback than the dmts for sharpening. The problem with them is they're more money and I'm not sure you get it back in longevity. http://www.chefknivestogo.com/atomaplates.html