With a little help from Wikipedia I have found two more classical singers from Puerto Rico, Amalia and Antonio Paoli, sister and brother. (Sounds Italian, right? The father was from Corsica (like Napoleon) and the mother from an island off the coast of Venezuela.) They grew up in Ponce, a Spanish colonial city, in the south of Puerto Rico. I visited Ponce several years ago. It is a charming city and a great producer of Puerto Rican rum.
Antonio had the more brilliant career of the two. He was born in 1871, dying in 1946 in San Juan. He was called 'The King of Tenors' and 'The Tenor of Kings'. He sang before many crowned heads of Europe during his career. Amalia was born in 1861 and became well known in Puerto Rico as a fine singer, receiving a scholarship to study in Spain. She was a soprano.
She managed to bring her entire family to Spain with her. Her brother, whose full name was Antonio Emilio Paoli y Marcano, was under the protection of Isabel de Bourbon, Princess of Asturias, the sister of the king of Spain. Thanks to Queen Maria Christina, Queen of Spain, he was given a scholarship to study in Italy. At one point he served the Queen as guard to her son, King Alfonso XIII. He studied at the Academia de Canto La Scala in Milano.
He made his major operatic début in Paris in William Tell of Rossini. The French newspapers declared that he should be named ' The Tenor of France'. During his career he was often compared to Enrico Caruso, singing throughout Europe, the Americas, and world-wide. Just before World War I he lost his voice and had a career as a boxer! Later the voice returned and he continued to sing and to teach voice.
Eventually, he returned to Puerto Rico where he attempted to start a Conservatory of Music which never came to fruition. This may explain the dearth of opera singers from Puerto Rico.
Justino Diaz was born in 1944, nearly one hundred years after Amalia Paoli, and has had a major operatic career. So far, these seem to be the major opera singers Puerto Rico has produced.