I rode around Ardgour with Mrs K last september. Went from Corran, camped at Glenfinnan and roe down Loch Shiel.
Yes, that track is ridable. It's a wide and undulating forestry road that in part is used by FC heavy vehicles for forest harvesting and gets a bit churned up but only in a small part of it. There are great views of Loch Shiel and surrounding mountains – mostly towards the Glenfinnan end but there isn't any technically challenging riding, unless…
There is an old coffin road that goes from Strontian to Polloch (the road climb it's an alternative to is pretty stonking). It is one of those 'curious, dotted line on map, maybe' potential routes. Geograph and google rendered very little information so I concluded that it's probably little used. Might be worth inspecting in dry conditions though. If you have a look at it then post back and let us know what it's like.