If you're not using core profiles, there's at least one other thing that can cause rendering to fail. the SDK uses clockwise winding of the vertices in the distortion mesh, so if you have face culling enabled, and your front faces are set to GL_CCW, then again, nothing will render.
You are a hero! 😄
This is a thing Oculus needs to fix, as the default order in OpenGL is counter-clockwise (GL_CCW). At the very least, the SDK renderer should disable (and reenable) culling automatically.