Revelation Dance inflicts damage and has no secondary effect. The type of Revelation Dance always matches the user's primary type.
Based on its description,
Baile Style - Fire
Pom-Pom Style - Electric
Pa'u Style - Psychic
Sensu Style - Ghost
it's obvious that the primary type is the type that appears first, as in Fire/Flying, Electric Flying and so on.
For Gardevoir, that primary type is Psychic, so it will be similar to Pa'u Style.