The CGS resolution given at http://www.cgsnet.or..._Resolution.pdf clearly states "Students are under no obligation to respond to offers of financial support prior to April 15; earlier deadlines for acceptance of such offers violate the intent of this Resolution." So (if the school in question is a signatory of the resolution) I think you should definitely report this matter to the CGS.
The CGS resolution is more than just a "gentlemen's agreement" among schools.