From what I have found it looks like they are the same people, only geographically separated and the different names just correspond to language/cultural differences by region. As it pertains to the Ilourians/T'loc'loc the difference seems to be what they call themselves (T'loc'loc) verses what they may be called by others (Ilourians), or Ilourians are the T'loc'loc of somewhere other than Silaar where the T'loc'loc reside.
Does that make sense? I guess it could be like "Indians" verses Native Americans (and/or the various names of the different ethnic tribes of the Americas). Genetically I think they are so similar that there are no game-stat differences.