You're mixing up two different things here. The Draconic Aura feat (Dragon Magic, pages 86-87) has a specified list of 10 different auras that feat can provide, and "Vigor" isn't on the list. The Dragon Shaman's Draconic Aura (Su) class feature (Players Handbook II, page 13) has a specified list of 7 different Dragon Shaman auras, including "Vigor". The feat doesn't grant Dragon Shaman auras, even though they have similar names.