Reduces the product formed from the reaction of NovW with dTDP-4-keto-6-deoxy-D-glucose to result in dTDP-5-methyl-L-rhamnose in the novobiocin biosynthesis pathway, an aminocoumarin family antibiotic that targets bacterial DNA gyrases. Binds 1 Mg(2+) ion per monomer. Antibiotic biosynthesis; novobiocin biosynthesis. Belongs to the dTDP-4-dehydrorhamnose reductase family.