The zip file for geofence-server contains 2 postgis jars.
They are useless, in that at the moment geofence-server uses an H2 DB.
Furthermore, they are harmful, since postgis-stubs-1.3.3.jar duplicates the PGConnection interface, also declared in the postgresql jdbc jar. The version in stubs anyway is missing a method, so if this jar is loaded before the postgresql one, it will throw
}} and GeoServer will not start.