Service Member's Occupational and Environmental Transparency Health Act or the OATH Act This bill requires the Department of Defense (DOD) to (1) record service members' exposure to occupational and environmental health hazards while deployed overseas, and (2) make such information available for post-deployment medical examinations and health reassessments. DOD and the Department of Veterans Affairs must update electronic health records with information from the Burn Pit Registry (i.e., a registry designed to track certain airborne hazards). The Government Accountability Office must submit a report evaluating implementation of the above requirements.