With all due respect to the above posters I have had a positive experiance with teaching Aikido to veterans with stress related disorders such as PTSD.
The syllubus is highly modified and features Aikido's Spiritual and nonagressive aspects of conflict resolution...
I however personally feel that a practice such as Tai Chi or similiar art would be more beneficial, and my suggestion would be to approach someone like Mike Sigman who is both a Vietnam Vet and expert on Chinese IMA.
PM me if you like and I would be happy to share my experiance with you.
I would also insure that the class be vetted by Licensed and Qualifed Mental Health Professionals.