As @Ryan780 mentioned, you can use the Google Assistant Relay to issue "Custom Commands" using my driver for the Google Assistant Relay NodeJS server.
Others have used this method successfully to integrate devices into Hubitat that are only controllable via Google Assistant. You simply need to prefix your command with "[CC]". For example, you would simply issue a "Speak" command to the assistant-relay device in the form of "[CC]Turn on Alarm" (or whatever voice command you would normally issue to a Google Home device.)
