I theorized perhaps the Observants mainly handles ghosts who rain enough destruction on Earth. Walker is the GHOST ZONE cop, so I assume he only handles ghostly matters that pertain to Ghost Zone rules and law and not of Earth.

As for the Fenton Jet Plane--gah, the plot and handling was just too stupid/unexplained for me to get into it, much like the majority of this episode. I mean, how does connecting metal hooks around Danny generate his powers? He's not a robot.