The 6th Edition rules state that although the ogre models are occupying two hexes, they are considered to be in the front hex for combat purposes.
Does that mean that other units can move into the second hex unharmed?
Yes. Just place the counter under the Ogre. As mentioned, the units (including the Ogre) are just representations. The Ogre "only" occupies the hex that its front is in. And, again as mentioned, all targeting should be directed at the front hex.