My iPad 3 shows the photos from my D800 as 'RAW+JPG' when they show up ready to be imported. However, on the iPad the NEF files do not show up and cannot be processed by any iPad application.
They can be transferred from the iPad to your computer and processed. I have a MacBook Pro, which runs an entirely different operating system to the iPad and can handle RAW files from all but the very latest cameras.
Apple updates the codec regularly, which is why Nikon does not need to put out an Apple codec as well as a Windows one.
Which doesn't explain the odd message on your iPad when trying to import photos from your D800E. I tried it using the USB3 cable that came with the D800 and it is working normally for me.
I have the camera set up to write initially to the CF card, with the SD card as overflow. So, wondering how yours is set up? Are you having the JPEG and NEF files sent to different cards?