I would have another chat with the vet....."snuffles" isn't a proper diagnosis. That is an old generic term that is a "catch all". If the diagnosis was snuffles, let me guess that either a sulfa drug or Baytril was prescribed....neither of which is very effective. Your rabbit is most likely suffering from an upper respiratory infection but other issues, especially dental issues, can mimic a URI. Even a piece of hay stuck in a nostril can do this. To effectively treat this condition, there has to be a sound diagnosis. I really hope your vet can give you a better explanation. And as far as being incurable, the bacteria that causes this is always there but can be managed easily by proper diagnosis and treatment. I have numerous rabbits here right now that have been surrendered due to "snuflles" and they are happy and healthy.
Randy