I don't think there would be any problem mixing the washed and unwashed fabric, but I would need to know more before deciding to wash the jelly roll. Do the chemicals in unwashed fabric give you any problems? Do you suspect that the dyes in the fabrics might run? Are you worried about the fabrics shrinking after you finish the quilt? If you answer yes to any of these questions, then you should wash the jelly roll - carefully! If you're not sure about shrinkage or dyes running, you could test the fabrics first.