Ok, the config settings of the router says it makes an analog measurement of pin AD2 every 100 ms and sends this as a broadcast, which ends up at the coordinator proven by the API packet. So there is RF traffic and there should be an RSSI pulse sequence generated. Atleast until 4 seconds has passed since the last packet.
The best would be to look at that RSSI/P0 pin voltage with an oscilloscope or logic analyser. But you probably don't have the latter, and I'm sure you would have considered an oscilloscope yourself if you had the chance. Maybe you have a multimeter (with/) or pulse frequency meter. Then you could tell that there is indeed a square/rectangular pulse coming out, or only a flatline high or low voltage.
Alternatively this forum thread on the Arduino site suggests that this 200 value in the pulsein command is too short. Which makes sense actually. Timeout at the 100% dutycycle is borderline. I don't know what kind of RSSI pulselengths or dBm values are to be expected though.