I'm not sure what you mean "attached to the ocean." It seems like if the altitude were zero, you would not see any light cast on the surface at all, right?
Lights in osgEarth are detected using the shader generator, and then rendered with a lighting shader. So no -- you cannot render a light without one of the lighting shaders. Phong is one, SimpleSky is the other. You can write your own lighting shaders if you prefer.