From this question we know the barge can be held at a set position with an accuracy of one meter or so. So the barge doesn't really move in the X and Y direction. This takes care of yaw as well. But that leaves 3 degrees of freedom: moving in the Z direction (up/down), pitch and roll.
None of these can be easily compensated for with the current barge design.
Does the stage have features that would help compensate for this motion? As the deck can't be counted on to be horizontal, you run the risk of having one leg touch down first. For the Jason-3 mission, the landing attempt failed because the lockout on one of the legs failed: would this lockout be applied before landing, or after?
Doing it before landing gives the opportunity to use the hydraulics to adjust the angle of the legs, at the cost of making the hydraulics more complicated.
Compensating in the Z direction would require a landing altimeter on the stage to get accurate height readings just before landing (GPS being less accurate in the Z direction).