Different things work for different people. The following should be of interest (this is a clickable link)
As far as the Apple Watch, series 1 and two don’t have location services.
The brand new Apple Watch Series 3 does have location services, but it doesn’t work the same way that a phone does. In order to help preserve battery life, instead of regularly broadcasting its location, the location is recorded internally and is available for query by approved apps.
That means that you can use “find my phone” to find an Apple Watch Series 3, but you can’t use Geopresence like IFTTT location.
So I’m guessing it won’t work with SmartThings, because you won’t get that “cross the border” Geopresence event. But I haven’t tried it to be sure, I don’t have a series 3 watch myself.
https://discussions.apple.com/thread/8094443?start=0&tstart=0
Location is only sent when someone requests to see it (it is not transmitted on a regular interval).