Yes, sourdough starter LOVES fresh milled flour! If this is a change for your starter, remember it may need some time to adjust. Every sourdough starter's microbiome is unique, so a change in the type of food it is used to eating could cause a few hiccups, but they will smooth over soon. For more interesting info on the factors of a sourdough starter's microbiome, you'll love my post on using sourdough starter straight from the refrigerator.