how does this compare to delta debugging[1]?

[1] https://www.st.cs.uni-saarland.de/papers/tse2002/tse2002.pdf

Delta Debugging provided a name and a generic algorithm for something that people had already been doing, but they hadn't been calling it anything and hadn't formulated it as an abstract problem.

DD just removes stuff. C-Reduce does lots more, such as inlining functions, rewriting the class hierarchy, instantiating templates, ...

More: http://blog.regehr.org/archives/527

Are "Test-case Reducers" different than "shrinking" in Haskell QuickCheck or Clojure test.check? I.e. are those libs useful for Fuzzing as described in the article?

Shrinkers, reducers, minimizers -- all are the same thing and all operate using the basic ideas outlined in the original Delta Debugging paper.

I'm not sure if the QuickCheck people have explored these ideas, perhaps they'll chime in.