I personally do not recommend the use of Dawn (or any) dish soap, alcohol or Neem Oil on plants, especially aroids.
Soap is a surfactant and a degreaser. It can damage the waxy cuticle of the leaf blade. The Dawn that used to be on TV washing the oil off the little birds in not the same Dawn we have now. They have added so many things to it, made it even more powerful, antibacterial, and its just not a really good option.
Alcohol is a solvent and a degreaser. It is very drying, and can also damage and even remove the cuticle.
Neem oil and other agricultural oil sprays are meant to be used on things like dormant fruit trees. They can and will burn the leaves if applied in too much light, and leave an oily residue that can clog the stomata (the pores) on a leaf blade and interfere with plant respiration.
Even though it may be enviromentally friendly, if you really like the plant, a better choice is to use a real insecticide meant to treat scale (or mealy bug, or scale).