Anodize and Electroless Nickel EN plating question
To answer your question, nickel plating would quotposionquot the anodizing bath, and anodizing would prevent nickel plating. So both would require the same amount of masking, but anodizing first would be safer, as the only result of a bad mask would be incomplete plating, where the nickel plating in the anno bath could cause burns in the aluminum.