While some that are on the bony points look like hock pressure sores, there are a couple that look like they are on places I wouldn't expect to see such injuries. In the "hollow" areas in front of the bony points.
I just might check for some kind of secondary infection, especially the highest spot towards the front.
Well, on second thought, they are on the same spot on BOTH legs so, I guess I would go back to being a place hit when the horse is rolling and kicking around.
There are hock shields that you can get to protect the hocks. Other than that, just keep them clean and protected with a antibiotic cream.
You can google hock shields for more info on them.