Theres the possibility of salmonella with just about any animal you own. Dogs, cats, snakes, mice, they can all carry it. Snakes just get a bad rap because there "icky".
You're probably talking about Ivermectin shots which are very real. Ivermectin is used for just about every type of mite you can name and is so common they sell it at farm supply stores. (At least around here).
I've heard of vets giving Ivermectin shots as preventive medicine. Although I've never been able to find anything that says it would actually keep your snake from getting mites if it was introduced to them. I honestly highly doubt it since to properly treat a snake with mites using Ivermectin you need to give the snake 1 shot a week for 3 weeks... Seems like if it could be used as a preventive measure you'd only need one shot.
David