Visible crew/equipment: In the library scene, when the ghostbusters are walking towards the old lady to ask her questions, if you look behind Ray's head to the right you can see a set light with a white tarp in front of it on the second floor of the library. (00:07:35)
Visible crew/equipment: When Dana arrives at the Ghostbusters' office, a crew member can be seen moving behind the filing cabinets behind where Janine is sitting. It could be Venkman, but even after Venkman walks over to Dana, there's still a rogue hand there, showing us it wasn't Venkman and was a crew member. (00:22:10)
Visible crew/equipment: Bill Murray and Dan Aykroyd's stunt doubles are visible in the shot (from behind) that shows the Ghostbusters falling into a hole. (01:20:35)
Answer: Ron Jeremy can be seen in the crowd outside the firehouse right after the containment unit is shut off.