I have personally owned a dwarf hedgehog, so yes, they definately do exist. Her legs were shorter than a typical hedgehog, and her face never grew out of the baby short and wide appearance. I can\'t remember what her adult weight was, but it was somewhere around 175-200.
She was also the smallest in her litter, she had two siblings that were completely normal, and by 3 weeks or so of age, the size difference was noticeable.
She did pretty well, but suffered from arthritis issues from a young age. I believe she was about 8 months old when she died.
On the other hand, I have also had baby hedgehogs that just failed to thrive whlie they were with the moms.... they were smaller than their siblings, but otherwise completely normal. These usually started growing once they were more dependant on solid foods, and by the time they were 4 months old, they had caught up with their larger siblings in size.
Any chance you can post a picture of him, preferably full body with face visible? I am curious of whether he is showing the same characteristics that my little girl did.