When you hire NPCs the only time you can be SURE of getting 100 % of a particular race is if you're at that race's homeworld. Otherwise, it's completely random. You can see which planet is the Homeworld by looking at the Race pages.
Some homeworlds are shielded, and controlled by a Faction. Contact those factions about buying NPCs of that particular type, and I'm sure they'd be happy to help you out.
...and even then you have a 90% chance of getting an NPC from that world.
You are entering the vicinity of an area adjacent to a location. The kind of place where there might be a monster, or some kind of weird mirror. These are just examples; it could also be something much better. Prepare to enter: The Scary Door.