The certificated flight instructor and student pilot were conducting a hover taxi in a Schweizer 269C helicopter, from the hangar area to a fuel pump, a distance of approximately 600 feet. The student was initially at the controls. According to the flight instructor, he took the controls from the student upon reaching the fuel pump, after the student stated he was uncomfortable landing on a raised platform in the confined area. The flight instructor landed the helicopter on the platform, where it then "entered into ground resonance." The flight instructor "rolled off the throttle immediately," but the ground resonance intensified, resulting in substantial damage to the helicopter.