You’re talking about zwave local scenes, right? Not zwave central scenes or smartthings scenes?
I don’t know about the SmartThings implementation, but zwave local scene controllers are not typically actionable. You can configure them, but you can’t trigger them.
The new Zooz switches have a new scene control feature where if you do a specific sequence it allows for scene control. But I’m not exactly which types of scenes this is supposed to be. This is what they say about it:
“You can trigger 2 scenes or control 2 independent Z-Wave devices in your network using this…” and work on “Scene 1” or “Scene 2”. Just by re-reading that, I’m guessing it’s supposed to be z-wave local scenes, but I’m not 100% sure… These devices already have working association capabilities.
OK, at the present time the smartthings zwave implementation does not technically support zwave central scenes.
So what your DTH has to do is to convert The central scene codes into “button presses“ and present itself to smart things as a button controller. So if your device supports 12 different central scene numbers then it would look to smartapps, including the official smart lighting feature, like you have 12 buttons.
You can see examples of this in the custom code handlers for the Homeseer switches, for example.
It won’t need a companion smart app. Once you have the DTH done, then it will just look like a button controller to any other smartapp, including web core or smart lighting.