Involved in the biosynthesis of capreomycidine, an unusual amino acid used by non-ribosomal peptide synthases (NRPS) to make the tuberactinomycin class of peptide antibiotics such as viomycin and capreomycin. Catalyzes the stereospecific hydroxylation of the C3 of (2S)-arginine to generate (3S)-hydroxy-(2S)-arginine. Usually clavaminic acid synthase-like oxygenases catalyze the formation of threo diastereomers, however VioC produces the erythro diastereomer of beta-carbon-hydroxylated L-arginine. It exerts a broad substrate specificity by accepting the analogs L-homoarginine and L-canavanine for the beta-carbon hydroxylation. 2-oxoglutarate + L-arginine + O2 = (2S,3S)-hydroxyarginine + CO2 + succinate kcat is 2611 min(-1), 831 min(-1) and 73.2 min(-1) for L-arginine, L-homoarginine and L-canavanine, respectively (at pH 8 and 30 degrees Celsius). Antibiotic biosynthesis. Belongs to the clavaminate synthase family.