Only thing rocky about the DFA and Dean Foods relationship is that Dean Foods owes DFA money and payment to DFA for anything owed before the Chapter 11 filing is pending and may never get paid in full. Dean Foods and DFA have worked hand-in-hand together on many crooked deals that resulted in screwing farmers and customers, so they've really been partners in crime and not adversaries. There are lots of court records and news stories that detail their past shady schemes.
As far as customers go, while Walmart is a behemoth there are too many regional grocery and c-store chains to name. Dean Foods shut down stores to offset any losses of Walmart and Meijer volume, the id–ts at the top just never understood that they needed to take into account the inevitable increases in distribution costs whenever a plant was shut down.