We are both in agreement that ADS-B OUT is required. But, I am referring to ADS-B IN which most military aircraft do not have as a matter of practice. If ADS-B IN was running in addition to ADS-B OUT on both aircraft then it might have provided additional situational awareness assuming the Black Hawk pilot was operating the helicopter properly. The original comment was about putting the receiver in listening mode and that's simply not possible with the Black Hawk.

I have been running an ADS-B receiver at home for 6 years via PiAware along with an AIS receiver. So yes, low cost :)