The 'maggot fly' is not sneered at by fly fishermen and is actually one of the best know fly's for grayling fishing in the form of Frank Sawyers Killer Bug. Fly fishing is becoming an increasingly broad-church and the old traditions are being challenged and to a greater extent swept away with the increase in popularity of Czech and French nymphing styles as well as the adoption of North American techniques (where they don't really give a damn about the rules and regulations imposed by 'our' traditionalists over 100 years ago).
If it's some material tied to a hook to imitate something that a fish wants to eat... its a fly!