Veterans Treatment Court Improvement Act of 2018 (Sec. 2) This bill requires the Department of Veterans Affairs (VA) to hire at least 50 Veterans Justice Outreach Specialists under the Veterans Justice Outreach Program. Each of these specialists must serve as part of a justice team in a veterans treatment court or other veteran-focused court. A specialist hired under this bill must be placed at a VA medical center that: complies with VA guidelines for specialist placement, works within a local criminal justice system with justice-involved veterans, maintains an affiliation with one or more veterans treatment courts or other veteran-focused courts, and provides specialists or establishes a VA-approved plan to provide specialists to serve as part of a justice team. The VA shall prioritize the placement of these specialists at medical centers that have an affiliation with a court that was established after this bill's enactment or is not fully staffed with specialists. The Government Accountability Office shall report to Congress on the effectiveness of the Veterans Justice Outreach Program.