Why don't you use Bind Variables for that query. I doubt that to_date exists for HQL.
Try the following:
Code:
String hibernateQueryString = "select reportsDto.teamRoom, " +
"sum(case when reportsDto.submitDate between :date1 and :date2 then 1 else 0 end) AS reportsDto.numSubmissions " +
"from ReportsDTO as reportsDto " +
"group by reportsDto.teamRoom";
Date d1 = .....;
Date d2 = .....;
Query q = session.createQuery(hibernateQueryString).setDate("date1", d1).setDate("date2",d2);
List reportList = q.list();