Exactly how can a cloak be gravitational? Perhaps cloaks work in the same was as shields, ie, deflecting the energy, however it deflects light in such a way to appear transparent.
Another possibility is like light can be bent in the atmosphere, the light around a cloaked ship is bent through an electromagnetic field. The charged particles may be arranged in such a way as to distort light.
After all, heat off a road can SEVERELY bend light, and no gravity is involved!