That is indeed what it looks like. I've never seen it that widespread outside the mouth though. It definitely has the look of stomatitis. Looks like it has already caused a gap on the side of his mouth too.

I would get him a to a vet asap. He can be saved.

You need to take a long hard look at your husbandry and the conditions in his tank. stomatitis is a secondary infection that takes advantage of a suppressed or overtaxed immune system. Take a look at what might be suppressing his immune system. Could be secondary to a respiratory infection too. You should probably raise those temps up near 90 degrees to help his immune system and do this day and night, but do not fail to provide a proper gradient. Too much heat and low humidity without a proper gradient can cause respiratory infections too, not just too cool and damp.

I wouldn't attempt to treat this on my own. Proper treatment as early as possible by a qualified vet is his best chance for recovery.