No, it won't harm Aluminum! Most carburetors are made of cast Aluminum and this product is made specifically for the purpose of cleaning them.
Don't know what the plating on your spark plugs was, probably Zinc Chromate or Cadmium. Chemtool won't hurt Zinc Chromate either, most carburetor linkages are plated with Zinc Chromate and they go in along with the body! And spark plug bodies are definitely not Aluminum, they are plated steel. How did you get from it removed the coating on a spark plug to it will attack Aluminum?