Can yoga help a person who has tight muscles, especially on the outer side of the legs?

Yes. I am a big fan of yoga and have an regular practice myself. Yoga is wonderful for tight muscles if you follow a few rules. First nothing done in a yoga class should be painful. If you are having pain, you need to back off of the pose. Second, make sure that you let the yoga teacher know of any physical problems that you might have before starting the class so he/she can adjust the practice.
Yoga for muscles. Yes. Proper yoga exercises can help you. If problem continues, see your physician for professional advise.