From what I have seen there are numerous pre-FTL species across the galaxy at varying levels of technology. Some of those may develop into FTL civilizations on their own given time but other more primitive species would take far long than the amount of time you would play to reach this state by themselves and thus would not become FLT during gameplay unless they are influenced into it. That said there are not minor races in the same vain as city states in CIV 5 or the minor races in Galactic Civlization as these pre-FTL species could each potentially develop into a full fledged AI nation. For instance it should be completely possible, if unlikely, for an AI nation to find and invade a primitive society and use the pops as slaves, the alien race just happens to be perfectly suited for many of the planets in the AI's empire and thus rapidly increases in pop count and then form a faction for freedom and wins becoming a completely legitimate space faring race in a relatively short amount of time.