Short post. I tried using a shortened URL in background-image, and it worked. Are there any cons with this approach?
The only thing that springs to mind for me is that you are making an extra HTTP call which would potentially slow you down. So instead of just requesting an image, you’re pinging a completely different server first to request the link to the image.
It probably doesn’t make too much difference, and once a user hits the site once you’ll likely have the image cached anyway.
You’d be better off not hotlinking all together, and then rename the image something as short as you like 
Now that you mentioned it, the image does take a bit longer to load when a shortened URL is used.