Quick search: I tried "Darget", "Valori" and "Palladion". No mention the poem under that name, and Darget and Valori in connection are named only once. That one occasion, however, does include the story which it looks like Fritz used as a very loose basis for the poem.

Lehndorff on August 10th, 1753: Darget gets his dismissal from the King. He was a man of low birth who had made his name through a beautiful deed when being the secretary of the French envoy Valori. When the envoy was staying in Bohemia in a small town, he was supposed to be arrested by a troop of Austrian husars. As soon as they arrived, Darget threw himself on the bed of his master after having hidden the most important papers away, and claimed to be the envoy himself. He was duly taken prisoner, and only when he was brought in front of Prince Charles - de Lorraine, younger brother of FS - the truth came out. Valori had hidden himself away in a small room and thus escaped a long imprisonment. His Majesty the King who always rewards valiant deeds took him into his service and made him his reader. He has held this position for seven years until his bad state of health made it necessary for him to return to his country. He was a man of wit and of all the Frenchmen at our court the least impudent.

So - his majesty sometimes rewards valiant deeds by writing satiric-erotic poetry about them?