That's such and interesting question. I am more familiar with the assertion that vegetarianism causes or is a symptom of mental disorders. This article showed an association, but evidence supported mental disorders preceded vegetarianism:
Michalak, J., Zhang, X. C., & Jacobi, F. (2012). Vegetarian diet and mental disorders: results from a representative community survey. International Journal of Behavioral Nutrition and Physical Activity, 9(1), 67.
I've been trying to find information to support persons with history of trauma, especially child abuse and/or neglect, are more likely to be vegetarian, due perhaps to identifying with animal oppression. I haven't found much, but the above article suggests to me there might be such an association (i.e., if the mental disorder was associated with childhood trauma).
I'm not sure I understand the rationale behind vegetarianism as adjuvant treatment for trauma, but I'm certainly curious!
Good luck.
Nancy R. Downing, PhD, RN, SANE-A
Associate Professor
Texas A&M College of Nursing Forensic Health Care
Forensic Nurse
Baylor Scott & White Medical Center