Theres a lot of references to ritual dances in the Saga's and Christian sources. Old tribal culture was very musical. Harald Hadrada (Hard Ruler) who was the quintessential viking ruler, wrote tons of Poetry and the guy had been a warrior king his whole life and even died on the battlefield. Most northern germanic and Scandinavian sources we have are songs and poems meant to be sung in the mead halls which was the center of their life. So I can fully get behind the dancing in this movie.