I am having the same problem here. I just purchased one of the new SmartThings 2018 Hubs (v3) and it’s unable to detect my HomeSeer WD100+ Dimmer.
I’m not sure the advice from @blebson is still relevant – I am not able to find any ‘Start looking for things’ button, or even the ‘Marketplace’ for that matter. I have already tried doing the manual reset on the HomeSeer switch (on // 3 up // 3 down // off) but that hasn’t worked. I’ve also added the WD100+ Device Handler (the one by DarwinsDen) to my web console.
From what I can tell, the latest version of the App doesn’t really have a button to force it to look for generic devices. When I go to “Add a Device” it spins and says it’s looking for devices, but the green light on the front of my Hub v3 doesn’t blink like when I’ve selected a specific device to look for. Further, because I can’t select to “look for a HomeSeer Dimmer” I can’t get it to blink/attempt to look.
I’m feeling like I’m going crazy here – these are the first dimmers I’ve found that don’t make my lights flicker, and now I can’t get them paired with my Hub!! Is this an issue with the Hub v3? Latest version of the App? any help would be greatly appreciated…