Why not trying to reason with them? They release the prisoners, break free from the Hertak, and are given the chance to be protected from them by the LSA and to develop past their barbarism.
Something tells me they are the race that is impressed by shows of force, and killing their master might be the ultimate form of that. Perhaps now they consider the Terrans/Cyrvans as more powerful than the Hertak.
But the Nordera probably don't want
to be freed. The impression I got of them is that they love fighting, and the Hertak gave them the opportunity to fight a whole bunch of other people. And the Hertak gave them spacefaring technology. They have every reason to like the Hertak, and no reason to desire protection from them. Technically, they are slaves, true, but they want to fight, and the Hertak want them to fight, so it's a win-win situation for both species.
It is possible that they see humanity/Cyrva as more powerful, but something tells me that they wouldn't like the idea of being peaceful all that much, which is what the Terrans and Cyrvans would require of them if they did ally.
Of course, the Terrans fighting the Cyrvans to a standstill despite the technology gap is pretty much the definition of "Humans are Warriors", which is surprising why it isn't on the WoD TVTropes page.
Well, then go put it there, why don't you?