Yes, that's no problem. Just plug an interface module into the nearest network jack--they're made by Global Cache, and called the "GC100". It has relay outputs, and you can wire one of the relays to the garage door switch. Then in your pluto-admin web site, add the gc100 device, and add a 'Generic IO Device' as a child of it. Both are listed under manufacturer Pluto. Call the Generic IO Device 'garage door'.
To control it you can add a scenario using the scenario wizard, and add the command to 'garage door' for on/off. That will add a button on the Orbiter to control the door. You could also go to the event wizard and add an event handler, such as "House changes modes" and "Armed", to make it close the door when the house is armed.
Of course with this wiring the relay will just effectively hit the button. Since most garage doors don't have a discrete open & close button, the relay will not work to force the door closed or opened. Also, you won't want the relay to hold the button down. So when you create the scenario, you could add the 'on' command, followed by a delay of 1,000 ms, and then the 'off' command. That way it will just press the button for 1 second.
A more sophisticated solution would be a garage door that supported discrete open/close commands. I don't know of any such model on the market. But the garage doors do have sensors to indicate if they are in the up or down position. So it would be possible to wire those sensors to the gc100's ttl inputs, and then have a DCE Garage Door device that supports a discrete open and close.