Thom,
If that relay's electrical ratings (current and voltage) are the same or higher than what the uncoupler electromagnet needs then you should have no problems. How does the unit work? You feed the power supply voltage to the circuit and attach the electromagnet coil to the output? How do you activate it? A momentary (doorbell-like) switch? You press it and regardless of how long you hold the button down the circuit will only supply the power for a predetermined period of time?