Harvesting on the Impassable

No true.  You'll just need to do more clicks to get to the desired square while starting from a harvest-able square.

Here, I think, is the correct method:

First, send an army to attack the impassible square - you do this by sending to the nearest passable square and using the red arrows to centre on the impassible square as in Wartow's method above.

Now, go to the military movements square and click on the coordinates the army is going to and harvest resources from there. In general, you can use this to send harvesters after an army to gather what the army will kill even though there is nothing harvestible currently there.

If you're quick, you can recall the army and the harvesters keep going. 

If it requires a "work around" such as URL manipulation then I would speculate that it is not a necessary part of any quest, mystery, or discovery.

It would be nice if this can be confirmed by System or other powers that be or have been.