What is the name of the villain group in Rayman 3?

The villain group in Rayman 3 is called the Hoodlums.

The Hoodlums are an army of hostile creatures formed after André, a Red Lum transformed into a Black Lum, begins converting other Lums to his cause. They dress themselves in rough, scarecrow-like outfits made from animal hair, giving the group its distinctive appearance.

Their invasion drives the plot of Rayman 3: Hoodlum Havoc, released in 2003. André wants to corrupt the world's heart and build an army powerful enough to take over the Glade of Dreams. Rayman and Globox oppose the Hoodlums while searching for a cure after Globox accidentally swallows André.

The Knaaren are a separate species encountered later in the game, while the Rabbids belong to a different Rayman-related spin-off series. “The Dark Creatures” is not the canonical name of Rayman 3's main enemy faction.