I too can't see how this cover can be seen as in any way related to disability. Perhaps Sondra can explain clearly how she reads the image in this way?
I always took it to be a shop mannikin figure of Nic showing his hidden material. and the dog does look to be burying rather than unearthing , but where is the disability aspect?
I personally don't like the cover because it is a rather feeble idea, a bit like those joke birthday cards which are funny for about 2 seconds and reading it is a corpse is a bit unsettling. On an album which is going to be around for ever something a bit more interesting would be in better keeping.
However it is a GREAT album and after a week or two most people would become oblivious to the cover art. Don't let it put you off!