The last picture of the burned spot look to me to be a large area. I would venture to guess that that area of his disk may be dead and starting to rot away. May be why its becomming see thru.
Now, two things in my opinion may happen. That area were he was burned may totally rot off up the the areas of the disk that are still ok. and he will then have a area of his disk that is just simply not there.
Second thing is, that area is healing and the body is getting rid of the bad stuff and will start to repair what it can.
But dont take that to the bank.. I have never seen nor delt with a ray that burned himself that bad. So rt now its just a waiting game...
This is what I would do::::: Just make sure he has a nice clear rock free spot to be. Change the water every few days.. add half the amount of salt you would for your size tank after every 4th water change.. and keep trying to feed him. Make sure any food that doesnt get eaten gets taken out later that day.
Just give him time and see what happens. With rays, they do slow breathing when relaxed. So, hopfully his pain is starting to go away and he is starting to relax some. If this is the case, eating is next.. Keep feeding the bloodworms and give it time.
I will say this, since its now been what, three and a half weeks since his accident and he is still alive, he is a fighter... Just give it time. Hopfully he starts eating soon.
With your bloodworms, if you are just dumping them in, try something different, take a turkey baster and fill with a few worms.. Not alot, but a good small squirt.. try placing the turkey baster under his disk without scaring him to much and squirt the worms out slowly.. that way they will be closer to his mouth and he might just take in a few...