Just a little addition to a great discussion. There are several known cases when autovaccination was partially effective against various pathogens in reptiles.
First one is the vaccination against Mycoplasma crocodyli in crocodile farms that is known since late 1990s: Mohan et al. (2001) Vaccination to control an outbreak of Mycoplasma crocodyli infection. Autovaccines also have been used against Crocodile pox.
Relatively recent research showed that auvaccination provides partial protection against Devriesea agamarum associated disease in bearded dragons: Hellebuyck et al. (2014) Autovaccination Confers Protection against Devriesea agamarum Associated Septicemia but Not Dermatitis in Bearded Dragons (Pogona vitticeps).
Autovaccine was also effective in treatment of Herpesvirus associated dermal papillomatosis in Williams’ mud turtle: Široký et al. (2018) Herpesvirus associated dermal papillomatosis in Williams’ mud turtle Pelusios williamsi with effects of autogenous vaccine therapy.
I’ve also read about the supposedly effective autovaccinations against Herpesvirus associated diseases in marine turtles, but with no scientific data provided. On the other hand an attemt to use vaccine against Herpesvirus in Mediterranean tortoises (Testudo sp.) has failed and there was no rise in antibody titer in vaccinated animals: Marschang et al. (2001) Virus isolation and vaccination of Mediterranean tortoises against a chelonid herpesvirus in a chronically infected population in Italy.
If we talk specifically about snakes there is a report on experimental vaccination against Reptilian ferlavirus (aka Ophidian paramyxovirus) in rattlesnakes. The antibody responses in animals were variable and transient, therefore vaccination currently could not be used for prevention or treatment of ferlavirus infection in snakes. Jacobson et al. (1991) Antibody responses of western diamondback rattlesnakes (Crotalus atrox) to inactivated ophidian paramyxovirus vaccines.