I just installed this, and I followed Pducharme's instructions to setup the properties file and it worked just fine. I did it by ssh-ing into unraid and using:
cd /user/appdata/unifi-video
sudo touch system.properties
sudo nano system.properties
and added the required line.
However, i could not get cameras to reliably connect to the docker.
I ended up installing a Ubuntu VM and running it on that and it works perfectly. Perhaps a port forwarding issue?