Can't remember seeing a dog at the end. Could it be the animal that played the role of Nigger?
As for ghosts, well I have one in my house and I've seen her, heard her and felt her. I see no reason why a dog cannot become a ghost although I find the evidence a little bit light in this case.
I've heard lots of stories of haunted airfields and I think there was a thread on this a couple of years ago.
The theory on how they come about is very straightforward. The heart generates a 12 volt 60Hz electric current, this powers the brain/mind and all its various subsystems. On death, the first law of thermodynamics says that this bio-electrical current should be dispersed into the local environment. In some circumstances, this law can get circumvented and this bio electrical energy does not disperse, it congeals and becomes self aware. That's easy bit.