I really can't see that this sensor is made by anyone else other than Panasonic, though Olympus seem unwilling to either confirm or deny that. It could, I guess, be made by someone else, but that does seem unlikely.
A reason for their reticence could be what they have inside the camera. This is from the cameras initial press release:-
"The refined image quality of the OLYMPUS OM-D is made possible by the new Live MOS Sensor with 16.05 megapixels and the TruePic VI image processing engine. The excellent noise reduction capability enables still image shooting sensitivity as high as ISO25600. The dynamic range has been expanded for more faithful reproduction of a wide brightness range. With its high resolution and excellent color reproduction, the OLYMPUS OM-D offers the highest image quality currently available among Olympus digital cameras."
Not many clues there. My initial feeling yesterday when I toook the pictures with the Voigtlander lenses was that I was looking at images with either no or a very weak AA filter. Something that has has aoused my suspicions about this is that on the occasional image at 100% magnification I think I see some slight signs of moire. This morning however, I'm not so sure. Maybe Olympus have found a way to avoid the softening effect of these filters while still achieving the same goals. If they had removed the AA filter altogether, this would surely have been something they were keen to let us all know about, but this didn't happen so there is something similar still in place it seems. Also I doubt they would be so coy about some newly developed technique or in camera software that makes the images look so good.
So, my final supposition, is that they have just done the whole thing very well. They have taken great care to squeeze the best possible quality from this existing sensor. If this is indeed the case, then they have achieved a high level of success, since the difference between results from the OM-D and the Panasonic GX1 are quite marked, and would, I believe, be clearly seen by non pixel-peepers also.
Whatever the reasons, Its certainly something that has put a smile on my face. I can't quite beieve my luck. After all this time I get a camera that looks and handles the way I want and also takes pretty astounding images as well. Perhaps my camera brand "wanderlust" is finally about to end?