The !kaf have all that. Nobody else. It works (or did, when it comes to the Stargate gates, but nobody can figure out how. I like the idea of having one species out there with Clarke's Law-level tech. The humans and other races are still using reaction engines (albeit powered by antimatter) and using spin habitats.

Hyperspace is my one exception to allow for a setting where trade and explortation can take place on a human timescale.

Most people do call them Greys. But since they have a spoken name, I used it. The Blimp's name for themselves is a complex pictograph. No spoken name, hence we had to give them one.