“The photograph was taken using the photographer’s equipment- therefore, it was a work for hire, therefore the photographer owns the copyright.”
If it is a work for hire, how much did the photographer pay the monkey to commission the work? Did they have a signed contract or just a verbal agreement?
The photographer could reasonably claim that he paid the monkey a banana, and that the monkey's acceptance of the banana relinquished any claim that the monkey had to the copyright of the photo.
The monkey would have to get its own copyright lawyer to put forward an opposing viewpoint.