The Sisters always talk about how they have a separate Writer's Workshop in addition to their D5/CAFE time, and they often refer to Lucy Caulkin's work. If you read Lucy'a writing about her workshop, you can see that it definitely fits in with the philosophy of the Sisters. I think you are spot on in seeing the connections between the two.
BTW, I have just recently been introduced to Lucy's new Units of Study for Teaching Reading, and again I see all the correlations between her work and the work of Joan and Gail.