I've heard about it from a very experience P.1 teacher. coz' my niece is very bright and she did skip the crawling stage. Now she's a P.1 student and she's having so much trouble with dictation and she always left things behind (since Sept she lost two text books already!) However, she's very good at maths.
My elder son skipped the crawling stage as well. However, he could read the Chinese characters of all MTR stations since he was in K2. He is in P1 now & he has no problem in Chinese & English dictations, but he's best at Maths.
I had seen in some book related to motor skill. They said that if a baby did skip the crawling stage. It is a matter of their gross motor function and affect their muscle strength and balance. And then affect their learning in school life e.g difficulty to sit properly (may be the child alway llie on the table), difficulty to write properly ( because of the muscle weakness). But you can strengthen the muscle by some specific exercise. And that is no relationship to dyslexia or learning difficulty.