I have SmartThings (~60 devices) and two Harmony hubs, which are linked to SmartThings and I just bought 2 Google Homes (is that how you make it plural??).
Here's how it works:
- When you link GH to ST, ST will present you with a list of all of your "switch" type devices (wall switches, dimmers, outlets, etc.) you can pick which ones will be exposed to GH.
- Once GH imports your list of switches, you can optionally arrange them into "rooms" in the GH app. (More on this in a bit).
- GH uses the names for the switches you have assigned in ST. You can also assign a "Nickname" in GH in case your ST name for the switch isn't something you want to say all the time.
- At this point you can say "OK Google, turn on the dining room light" or "OK Google, dim the family room lights" etc.
It all works very smoothly. The only issue I have been seeing is that if you have multiple names that are similar, it might assume you want them all on/off together. For example, I had three switched named "Kitchen Lights", "Kitchen Door Light", and "Kitchen Door Outside Light." When I use the kitchen I only turn on the first one - the door ones are rarely used. However, when I would say "OK Google, turn on the kitchen lights" - it would turn on all three. It's "smart" in that it parses the light switch names and guesses that I actually have three lights in the kitchen and I want them all on. So, I had to assign nicknames for the other two so they didn't have the word 'kitchen' in them. I'm sure this will get better with time.
More about the rooms: The rooms construct is there so you can group things together and turn them all on/off together. So if you had Table Lamp, Overhead Lights, and Accent Lights all grouped in a room called "living room" you could turn them all on by asking google to turn on the living room as well as accessing them individually by the individual switch names.
I mentioned that I also have two harmony hubs connected to ST as well. The Harmony activities appear as "switches" in ST so they too can be started/stopped via GH. "OK Google, turn on the bedroom tv"
One small caveat, at present, GH cannot run ST routines directly, but there is an easy workaround. Simply, create a "Virtual Switch" in ST, then use a smart app that triggers the desired routine when the virtual switch is flipped (ST has this smart app in the marketplace). Since GH sees the virtual switch just like any other switch, it works great.
I also have a Nest, which the GH can control directly.