In the UI, they are depicted as a different device type ("urn:schemas-garrettwp-com:device:ISYFanLinc:1") but the expose the service "urn:schemas-upnp-org:service:Dimming:1" for control.
In HomeWave, I can create a dimmer control, and it shows the fans as assignable. Once I assign them, they are controllable and will update, and based on the percentage they get set to hi/med/low/off.
High LoadLevelStatus = 100
Med LoadLevelStatus = 75
Low LoadLevelStatus = 25
Off LoadLevelStatus = 0