Most engines have their graphics engines. Say ogre3d.. Is it basically a wrapper for OpenGL?

Yes. Generally you'd call these a "wrapper" if they don't do very much to change the underlying abstractions/interfaces -- e.g. if you want to use GL from C#, you'd use a C# wrapper of GL, and you'd expect that the functions provided by the wrapper would be quite similar to the real underlying GL functions.

When a wrapper starts to change the interfaces, and introduce new higher level abstractions, like "models" and "terrains" and "shadows" (instead of vertex buffers, and shaders, and draw-calls, etc), then you'd call that "wrapper" a "graphics engine" instead.