Ok, so I found a deer pelt earlier. I only noticed it was different from a deer hide when I went to turn it into leather.
It's the same weight and has the same value as a normal deer hide, but it can't be tanned. It also isn't dropped by anything, and apparently there are only 12 in all of Skyrim.
So does it have a use, or is it just something to collect, like spigots?