Yes, it is. I attacked Jake with a knife a couple times, with and without Shield Expertise. Without it, the damage was all within the stated 5-13 damage range; with the skill at level 3 (24+20 damage), there were damages listed in the 27-37 range. The damage is in red (same as weapon damage), with no sound or visual effects to indicate it has kicked in. I'm going to check something else in a bit....
