The fan is still a motor: the physics are different than a bulb. But if it’s a small enough load and it’s just an on/off switch, you’re probably OK.
As for the integration part, Smartthings is in the middle of a huge transition. Under the new architecture, smartthings will no longer host groovy code. Instead, you can write whatever code you want, host it yourself, and come in through the API. So much more like what everybody else was doing.
That should work for any switch of any protocol connected to your SmartThings account. (That’s the front door to the new ST architecture)
If, as you’ve described, you also want to be able to go directly to the switch through the switch’s own API, but do polling through the ST API, you should be able to do that with one of the Shelly WiFi devices. Just make sure you get one Spec’d for US wiring, they are available in a number of different countries.
Connect it to your ST account through an Edge driver and it will appear on the list of devices available through the ST API, as well as still being available through its own API.