This project demonstrates how to make a native OpenGL Framebuffer object on iOS and pipe the resulting texture output to a Unity texture.
The code is heavily commented, and littered with GL checks, so if you run into GL errors, you should be able to track them down.
The example shows a native OpenGL texture being created and rendered to an FBO. The output from the FBO is rendered to a Unity texture. The Unity texture is then used in two different materials on two different objects in a scene.
Each frame an update is called that changes the image that goes into the FBO, causing the resulting Unity Texture to animate.
This is the Xcode project containing the plugin code. When you build this a post build script will copy the required files to the Unity 3 and 4 project files
The Unity 3 version of the demo.
The Unity 4 version of the demo.
Both Unity demos are the same except that 3 uses a plane and 4 a quad.