Irv, if you meant 1 horseshoe shaped single large piece of plywood instead of 3 smaller pieces, sure. It'll take a lot of a 4X8 sheet, 3 small pieces wont use nearly as much. And you could still use separate seat cushions.
If you meant a single large triangle shaped piece that fills the whole bow area, then, no, I wouldnt unless its necessary for your interior remodel.