Pretty much my exact thoughts
In terms of Dancer and the girl in the video potentially being a Dancer, another idea is potentially Advanced Jobs. You unlock the new job with the level 60 of two other jobs. It could explain why she seems so similar to Monk in some respects, but so different in other ways.
Level 60 Bard + Monk = Dancer
Level 60 Ninja + Dark Knight = Samurai
Level 60 White Mage + Black Mage = Red Mage