SharpTools can interface with Google Assistant Relay and Cast Web API. If you have the related devices created in SmartThings, you can authorize them in SharpTools and then use them in either the dashboards or Rule Engine – a common approach being to expose the custom commands from these integrations using Variables + Rules and then interacting with those from your dashboard.
For Google Assistant (voice) integration, I’d be interested in better understanding what you’re looking for there that isn’t already supported by your connected platform (eg. SmartThings / Hubitat).
Google recently announced their devices API (eg. Nest Thermostat, Camera, etc) and it’s still early times for that. You can express your interest in a native SharpTools integration here: Google's Nest Thermostat API's
And since we’ve split this topic out from the original topic, I’ll mention it here that Google does not currently provide an API for the devices that you integrate into Google Home (eg. C by GE bluetooth bulbs). 