If a game has one end of a wormhole but not the other, is that hex with the wormhole considered a wormhole space for things like the "Ghost Ship" action card or objectives that require you to have ships in a wormhole space?

Ki_Ryn said:

Per the rules, if a wormhole doesn't have a partner, it is ignored, and treated as if it wasn't there at all. That means that you cannot use it for Ghost Ship, nor must you possess it to qualify for Keeper of Gates.

Note, however, that an easy way to mitigate this is to either just ensure that all wormholes are in play, or include the Wormhole Nexus; though the Nexus isn't required for Keeper of Gates, it does count as another end of a wormhole so that you won't have to worry about it being too easy.