@nickf called me out for not having iPad templates in the Konigi OmniGraffle Wireframe Template, so I got off my lazy ass and added some since this thing hasn’t been updated in over 2 years! Added iPad Portrait 1 up, iPad Portrait 2 up, iPad Landscape 1 up. They have guides for 2×2 or 3×3 grid.
Note, this is for OmniGraffle Pro ONLY. You will not be able to edit shared layers to modify the headers and other templates. Get yours.