It sure can't hurt to mass balance the stab. If the stab's center of mass is forward of it's mean aerodynamic center, it probably will not flutter. Helicopter rotors often have weighted leading edges of the blades for this very reason. The higher the airspeed, the more important it is for each part of the plane to be aerodynamically stable on its own as well as having the entire plane being stable.
If the stab's pivot point should also be slightly ahead of the M.A.C. or control snatch can occur.