I've made a few amateur maps in the hammer editor, and as such I know the ropes of the program. There is no way to edit bsp files from hammer, but you can decompile them using external software. Going through the map, there is no script, no entity, nothing that would suggest any form of creature to be added directly into the map. All of the people you hear saying there are ghosts are simply lying and faking people into believing this overdone bait.

There are no ghosts, there are no creatures.