According to page 97 of the sixth printing of Tactical Operations: Advanced Rules, a unit equipped with an active probe reduces the to-hit modifier for firing into or through woods/jungles by 1.
When using the Woods Cover rule found on page 82 of TO:AR, the woods/jungle hex occupied by a target does not apply a to-hit modifier at all. If an attacker has an active probe and there are no intervening woods/jungle hexes, does this mean the resulting modifier is -1, or does it mean that the active probe applies no benefit?