Flatline sustain LED

[shooter_mi]

I built John Hollis's flatline compressor today. This circuit sounds great. I used a VTL052.

Out of curiosity, I placed a LED in parallel with the LED side of photocoupler. My hope was to have an LED that could be panel mounted and provide an indication of when the compression kicks in. The compression continued to work, and to my ears there was no change in tone, but the LED didn't illuminate. Then, again out of curiosity, I removed the phoocoupler (I had it socketed) and replaced it with another LED (I left the LDR side empty). Both LEDS illuminated when receiving signal.

First question: Why will an LED in parallel with the LED half of the VTL052 not illuminate?
Second question: If I ditch the VTL052 and just match an LED to an LDR, I can make this thing do what I want, but does adding a compression indicator LED in parallel with the LDR/LED pair compromise the circuit?