Stephane not trying to argumentative I think this part says if the LOS crosses a bocage hexside and you are not adjacent they must be spotted.
If it's a open-terrain-type hex (w/ Bocage hexside) and the enemy LOS crosses the Bocage hexside and the enemy ISN"T adjacent, then the hex must be spotted before it can be fired upon.
No problem Art, pobably my poor english skills showing
I don't have the HON rulebook in front of me but I'm pretty sure that if you would be otherwise spotted in this open hex (by adjacency, being marked with a Fired, moving, etc.), then you are spotted and can be fired upon. If this was not the case, then, to answer your original question, you could never opportunity fire on a moving unit adjacent to a bocage hexside because you can't spot while they are on the move.
Usually, you are considered spotted because you are marked with a Spotted marker, a Fired marker, moving, adjacent to an enemy unit, standing in the open and so on. What the bocage does is that it requires you to be spotted, regardless of the terrain you are standing in, if enemy LOS cross the bocage hexside.So, unless you are spotted by other means than simply standing in the open, your opponent does have to spot you. Without the bocage hexside, he would not