i've lagered some beers and i keg, but i force carbonated them. here's my schedule for lagers:
once brewed, i pitch the yeast starter into the wort at as close to 70 degrees as i can get it. once i see visible fermentation, i move it into my chest freezer with the external themrostat set at the desired fermentation temp range (the lower end of the range is best). let it ferment out for about 12-14 days. then i raise the temp on the thermostat to about 66-68 degrees for a 3 day diacetyl rest. i rack to secondary, then lower the temp by 2 degrees a day until i reach 30-32 degrees. let lager for at least 4-6 weeks. if you lager for more than that, you probably will not have enough yeast to carbonate. some will add a neutral dry yeast when bottling so it will carbonate. if you don't lager for more than a month or so, then drag the racking cane along the bottom of the secondary to stir up some of the settled out yeast when transfering to the priming bucket or keg. i force carbonate mine, so i don't have to worry about having enough yeast.
and to answer your question, in my opinion, i don't think lagering a carbonated beer would give you the lager characteristics your looking for in a lager beer. you can lager in a corny, then jump it to another when your ready to carbonate. just push it from one keg to the other using the co2. it's actually better do do it that way, because it's less exposure to light and air. i don't know about how German brewers did the Marzen/Octoberfest back in the day, but i know they don't carbonate lagers prior to lagering today.
did that help any?????