Sewernose de Bergerac is a nod to Cyrano de Bergerac, the eponymous character in Edmond Rostand's famous play.
Sewernose de Bergerac's sewer hideout is a reference to the famous urban legend of alligators in the sewer.
Monterey Jack calls Sewernose de Bergerac "battier than a case of Jamaican Fruit Bats." The rangers had fought Jamaican Fruit Bats earlier in the series.
The female opera soloist is dressed in the famous Valkyrie costume from Richard Wagner's opera, Der Ring des Nibelungen. That appears to be where the similarities end. The plot of the opera the rangers watch differs dramatically from Wagner's work.
The scene in the season 2 intro video that features a fencing alligator comes from this episode.