Button to kill power to BL1500

We have an estop button and want to kill power to the BL1500 controller when the button is pressed. The button could control power to a mechanical relay which would kill the input power to the BL1500. However, we want the button to control a high side N-channel FET controlled by a gate driver and the Roboteq input power would be gated by the FET. Is this application ok or could our FET (or Roboteq) be destroyed if power is suddenly removed while powering a motor?

In theory, there is no reason it wouldn't work.
Make sure you use a very low RDSon MOSFET, however. The on resistivity may cause added stress to the internal capacitors. Monitor their heat during operation to be sure there are not heating.
This shut down method should be used only for emergency. Grounding the power control wire is the correct way to shut down the controller.

Thanks. We will also be using the power control wire to shut down the Roboteq. Now that I think about it, how does the Roboteq shut down on the power control wire? Is this just a digital input into a micro or is there external circuitry that guarantees the motor fets are off even if the Roboteq micro or the Xilinx chip fails? If we can trust this Roboteq shut down, we might be able to avoid using an external fet to kill Roboteq power.

The power control goes to the shut down pin of the dcdc converter. It will effectively kill the internal supply voltage to the logic and to the MOSFET drivers. It is a very safe way to stop everything as long as the hardware is not damaged.
If the mosfets failed in a on state, it could conceivably happen that the motors would be on after such a failure. We have never seen a report of this ever happening but to be safe it is always best that the emergency shut down switch be separate to the controller