You can still sometimes find the quirky outlink although I think it’s been officially discontinued. It will work with smartthings although you won’t get energy reporting. And there have been reports that it drops off the network from time to time.
Otherwise you can use one of the smartenIT relays ( there’s a single, double, and a heavy duty), those all work well with SmartThings.
The relays say they work with ceiling fans, but that’s only for on/off, not variable speed control. You can check with the company to see if there’s anything they recommend, they’re very reputable.
Another option for fan control, although it’s expensive, is to get the Lutron Maestro IR wall switch, which gives excellent fan and light kit control, and then control the switch with harmony.
Harmony runs on Wi-Fi and has an IFTTT channel, so that gives you IFTTT control of the fan.
This is a well engineered device, excellent ratings, it’s just that it’s expensive. $100 for the switch and another $100 for the harmony. And the switch is an IR device so you have to be line of sight to the harmony, you can’t use a harmony back in the main house.
Good point, I misheard the original post and have updated mine above.
As far as the 2 hubs communicating, this is covered in the wiki article on automating an outbuilding. You can use IFTTT as a man in the middle, but at the present time they each have to have their own IFTTT Account and then you use email or text to communicate between them.
So it’s clunky but doable. I believe the OP had already considered this option.