Heather Morris actually is a professional dancer. She was on tour with Beyonce and hired to teach Chris Colfer the Single Ladies dance. When they decided to add another Cheerio, Ryan Murphy said, "Hey! How about that blond dancer?", and that's how she landed the part of Brittany. I would be surprised if they had to find someone else to do her dancing.

(hides in shame at total and complete gleekness)