Richard is only partly correct.
ESU have said that they have tested the LK200 with the ECoS and found that it works without any problems.
BUT, and this is the important part that Richard ignored, you said that you want to detect occupancy in the reverse loop, and that is where you will run into trouble. The ECoSDetector works by sensing the current being drawn by the decoder in the loco on the occupancy detection section. The LK200 is an active device and draws a small amout of current even when there is nothing in the reversing loop. So when you install the LK200 between the track and the ECoSDetector you will find that the ECoS shows the reversing loop as permanently occupied because of the current draw of the LK200 itself in its idle state. You cannot get round this by installing the LK200 in the supply to the ECoSDetector.
To summarise, any reversing module that draws current even when the reverse loop is unoccupied is incompatible with ECoSDetector.
The only work around is to use some other method of detecting occupation in the reversing loop. In theory IRDOT or similar would work if you used the output from it to complete a circuit connected to one of the non-railcom track ports on the ECoSDetector, but this circuit would have to include a 9k Ohm resistor to limit the current in the circuit. Without the resistor when the IRDOT controlled circuit was completed there would be a complete short and the ECoS would shut down.