The fact that it's fragmented would make it an excellent arbitrage opportunity for a physical OTC trader. Especially since the traders at the smaller producers are typically not well paid so they have less motivation to seek out the best price. A prop trader at Cargill or Koch Would be much more active and aggressive.
I think that's true, but in the case of RPMG (link below) it looks like some of the little guys realized their limitations and formed a multi-plant ethanol and DDGS marketing/trading firm.
http://www.ethanolrfa.org/pages/useful-links (scroll down to ethanol marketers). There are at least three marketing/trading firms that don't own plants and I can think of two more.