matt,
They are, indeed, checking for ice following deicing. However, a peculiarity of the MD80 series is the tendency to form ice on the top of the wings in high humidity conditions up to 10/15C due to the configuration of the fuel tanks. If there is cold fuel in the center tank ( which extends 5 feet outboard of the fuselage on each wing ) in contact with the upper surface, the upper wing may get cold enough in this area to cause ice to form in high humidity conditions.
Some carriers have installed electric heater blankets that operate on the ground to prevent this happening. The blankets, however, are not used ( turned off ) during environmental icing like snow, frost, etc., as they allow ice to melt , run back, and refreeze causing other problems. Absent the heater blankets, the visual inspection is still required when the temp/humidity conditions are favorable to ice formation.
And, the inspection by ground crew is still required after deicing to verify the effectiveness of the procedure.