It's said that trolls lower than purplebloods sleep in recuperacoon to prevent nightmares against chucklevoodoos. That means violetbloods and fuchsiabloods don't need to sleep in recuperacoons?

No idea actually, I couldn’t find anything regarding Seadwellers aren’t affected by Chucklevoodoos. Purples are an enforcer Caste, and while Seadwellers rule the empire, the world is more controlled by Purples than Violets or Fuchsias, so they may still affect them, with Fuchsias being a likely exception.