Lots of Strictly celebs have been trained dancers to some extent - Jill Halfpenny, Aleisha Dixon, Patsy Palmer, Matt di Angelo, Jason Donavon, Natalie Gumede...
In this series, Frankie Bridge went to stage school and studied musical arts and I'm sure Simon Webbe has had dance training.
If they've been to stage school they will almost certainly have had dance training. If they've been acting on tv, film or on stage they have experience of performing in public. If they are sports people they don't have the performing experience but they do have stamina and agility.