Ive never made a blue jean rag quilt but ive seen lots where the layers were (bottom up) blue jean then batting then cotton/flannel. So yes, by all means you can rag the not denim side. A quick google image search shows lots of folks doing just that, probly makes for an awesome picnic quilt. (No, no slothy... No more planning, you are far. Tooo busy)
And its your quilt. Sew em into four patch blocks or rows, eventually it all looks the same.