Allies of the Cardassians, the Valerians supplied the Cardassians with weapons-grade dolamide during the Occupation of Bajor, and it was suspected that they continued to do so after the end of the occupation. Their typical route in conducting this type of trade included the planets Fahleena III, Mariah IV, and Ultima Thule. The Valerians were also trade partners with the United Federation of Planets.
According to the episode's script, the Valerians were simply described as "humanoid with minimal prosthetic."
According to Star Trek: Star Charts (p. 46) and Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), there was a star system named Valeria, which might possibly be the system of origin for this species, in the Alpha Quadrant. This was a binary system with a pair of G-class stars. In the late 24th century, it was an independent system.