Well, the whole idea behind the ghosts in the Ghostbusters' world is that they're able to exist because they're made up of the negative energy that was left over from a rather unpleasant death. These ghosts are NOT HAPPY. They're not really interested in communication, they just want to make people as miserable as they are until they feel that the wrongs that were done to them have been righted and they can finally be at peace.

These are the ghosts that the nasty slime has released into Mayfield. It wouldn't be able to summon "happy" ghosts.

Any ghosts your character might come across will be very angry and probably capable of speech but simply not interested in talking. It will only be interested in scaring the poop out of anyone it meets and possibly even doing damage if it's a more advanced spirit capable of manipulating physical objects.

So if the ghosts from your character's world are angry? Sure! And they're probably capable of talking, they'll just be inclined not to unless seriously provoked.