Would it be possible to query VM running state from a docker container?
Are there any temp files or sockets that could be passed to container for detection?

ssh into the Unraid, use virsh commands. This assumes your container has ssh, or ssh can be installed in it.

 

or, ping the VM's IP to see if it responds.

 

I can think of numerous ways to get info, but without a specific use case it's tough to suggest what the best method would be.