After ten years working with under-fives, I have LOTS of positive stories of littlies who didn't crawl at 8 months. Or 10 months. A few from 12 months. One as late as 16 months. I wouldn't be in the slightest bit concerned about it.

Tummy time - some kids do just hate it. It's not a BIG deal. As someone said, they can be taught to crawl later on - even 18 months is a fine time to learn to crawl (and what kid wouldn't want to get through a tunnel, into a cubby etc at that age?)

My sis was a non-crawler. Bum shuffling was just more efficient for her. She's working on her second degree at the moment. Sure, she's flaky and a little absent-minded, but that's personality. She certainly never had ADD.