From the atc perspective, any aircraft that has recently departed and asks to return to the airport I consider an emergency, period!!! Until otherwise informed.
The fire and rescue companies at JFK would ALWAYS and I say again for emphasis ALWAYS rather be at the runway ready for a problem, than have to react. When atc requests a response the fire trucks respond and in my career I have never been nor have I ever heard anybody else questioned as to the validity of the request.
Aircraft at JFK do not return for fun. It's my job to get you back to the airport as fast and as safely as possible, I will do that first and ask the reason why later. You have a good reason, I'm sure and when the flight crew has the time and inclination they will share that information but from the controllers perspective, at least initially, it is not germain.