In theory, i'd say yes. It gets rid of the ice resistance to make a weakness, and thus it doesn't have the ability to resist ice, giving the weakness to flying as well as the weakness to water.
I ran a test here. Shock wave did about the same amount of damage, and it has nearly the same base power. So far, yes.
>0 SpA Sunkern Freeze Dry vs. 4 HP / 0 SpD Gyarados: 84-100 (25.3 - 30.1%) -- guaranteed 4HKO
0 SpA Sunkern Shock Wave vs. 4 HP / 0 SpD Gyarados: 84-100 (25.3 - 30.1%) -- guaranteed 4HKO
On that calc, I can set the base power of Shock Wave to be the same as Freeze Dry. It appears that Freeze Dry does in fact do 4x damage to Gyarados.