Do they use hyperbaric oxygen therapy at veterans hospitals for the vets that have traumatic brain injuries?

Doubtful: There is some anecdotal evidence of it helping various brain syndromes which may result from swelling or poor perfusion, but usually this will have the most beneficial effect early in the disease process. As there is no concrete evidence, insurance will not pay for such therapies, and treatment can be costly for private payors.

Being studied: I believe that dr. Tyson is correct. See: http://www.Va.Gov/vatap/docs/hbotbiiptsd2010tagm.Pdf (bibliography update: hyperbaric oxygen therapy for traumatic brain injury and post traumatic stress disorder).

Still being studied: So far, nine peer reviewed publications have provided little evidence of the benefit for HBOT for TBI. Some people in the studies did improve, but this improvement was consistent with what one would see with a placebo effect . There is at least one ongoing study, so right now, the answer is no, the VA will not be using it routinely, but this could change if empirical findings support its benefit.