Yes, Rainbow Dash is Fluttershy's father.
It's my headcanon, I can do with it what I want!

I'm actually rather proud of myself for this one. Somehow it ended up being good.

His father's son by Miracle of Sound ( https://www.youtube.com/watch?v=LbkBEWh5PIs )
My Little Pony: Friendship is Magic is owned by Hasbro