Create a marker at two locations and place the hostage at the third. Make them type empty so that they are invisible. Group (or is it Synchro?) the markers to the hostage, who will appear randomly at either his start position or one of the markers.
Create your little camp and guards anywhere. Use setPos commands (relative to the hostage) to make them appear where the the hostage is.
When the marker is to appear on the map, setPos one of the markers you have already used to the hostage's location and use setMarker commands to make it appear as you want. (Set the text in the mission editor, it's invisible at the start so nobody can see it.)