From the Foundation for Medieval Genealogy page on Anjou:

http://fmg.ac/Projects/MedLands/ANJOU,%20MAINE.htm#FoulquesIIdied958A

DROGON d'Anjou (-998). The Gesta Consulum Andegavorum names "primogenitus Gofridus…Guido…episcopus Podii…tertius minor Drogo" as the three sons of "Fulco Pius", specifying that Drogo succeeded his brother as Bishop of Le Puy[90]

However, according to the French Wikipedia page of his father, Foulque II d'Anjou:

http://fr.wikipedia.org/wiki/Foulque_II_d%27Anjou

Dreux or Drogo is named by some as a Bishop of Puy, succeeding his brother, but the list of bishops of Puy does not mention this name in the 9th century, and his presence in genealogies is probably from the confusion with Drogo of Brittany, son of Roscille de Blois and Alain Barbetorte, and stepson of Foulque II (he became stepfather when he married Roscille, widow of Alain).