Answering my own question.
I installed these packages to my unRAID 6.1.6 server. (Copy them to /boot/extra and reboot or use installpkg command):
python-2.7.11-x86_64-1
python-netifaces-0.8-x86_64-1alien
dnspython-1.10.0-x86_64-1alien
openssl-1.0.2e-x86_64-1
..then got the latest version of Sleep Proxy Client from https://github.com/awein/SleepProxyClient and copied it to the flash drive. Since I'm using the Dynamix S3 Sleep plugin, I added the following to Custom commands before sleep: in Sleep Settings
python /boot/wherever/you/put/yours/sleepproxyclient.py --interface br0
Now when my unRAID server goes to sleep, the Airport Express on my network registers the smb, afp, sftp, ssh services for my unRAID server. For example if I try to establish an ssh connection to my server, it wakes up. Or if I try connecting to any of my SMB shares, it wakes up. Great for file services etc...
But...
Unfortunately any of the services that are running under docker does not register with the Sleep Proxy this way. When I run sleepproxyclient.py --debug, I don't see any of the docker services as advertised..
I'd love to be able to have at least my PlexMediaServer docker register its services so that any attempt to connect to the PMS when unRAID is sleeping would wake it up.
Any ideas as to how I should go about enabling dockerized apps to register using SleepProxyClient?