DD1 hated tummy time so i never bothered forcing the issue (much to everyones disgust) and she began crawling not long before she turned 6 months old.....was rolling heaps from 4 months....so for her no tummy time didnt stop crawling.

DD2 hated it so i never forced the issue and never wanted to roll until 7/8 months and now at 9 months has jsut began trying to crawl.

Both my kids are very different and no tummy time had no impact in my opinion.