There are certainly ballets galore set to ballet music from opera: Balanchine's Ballo della Regina from Verdi's Don Carlos (the French version); Donizetti Variations (from Dom Sebastien); Sonnambula to Bellini music from La Sonnambula & other of his operas (wonderfully stitched together by Rieti for the ballet); Robbins' Four Seasons from Verdi's Les Vepres Sicilienne - the French version of I Vespri Siciliani - along with some I Lombardi & something else which escapes me for the moment.
For Ballo, Balanchine loosely used the theme of the ballet in the opera. A ball is given by King Phillip to honor his bride, Elisabetta (Isabella, actually but that's off subject). A ballet is part of the entertainment. It is about undersea creatures who find a great pearl - La Pelegrina - which Phillip then presents to Elisabetta. Centuries later Richard Burton presented La Pelegrina to another Elizabeth.




