Ligon II was another Capella IV. It had a substance the Federation needed, so the law was bent just enough not to tweak the PD's nose, while ensuring that the substance was obtained. (Ligon II was from the episode "Code of Honor".)
Keep in mind that despite certain cultural trappings, Ligon II was a technologically advanced civilization. They were backward compared to the 24th-century Federation, but they had their own, independently invented transporter technology, they had an "orbital control station," and they had those energy-beam thingies in the combat arena. We also know that at least one Ligonian was on Earth in the 2320s, perhaps even as a Starfleet cadet, since Picard wrestled one in his Academy days according to "The First Duty." So apparently they were a spacegoing people. If they had transporters and orbital stations, it's reasonable to assume they'd independently developed warp drive as well.