It will work with this integration.
I don't typically use the Harmony activities, the only one i have is for my basement receiver. I expose the harmony hub as a switch to google home and then add switch, volume, and brightness traits. From the home app I can turn the receiver on/off and adjust volume up/down with the brightness adjuster. With Voice control and google smart displays you can turn on/off, adjust volume up/down, and mute/unmute.
You could also expose it to google as a media device but then you can't use the brightness trait to adjust the volume.
