I have had over 20 blues of various size with cerith, astrea, and mexican turbos. NOT A SINGLE SNAIL DEATH FROM HERMITS. The blues outclean the reds, are not aggressive and have not killed a single occupant of my tank.
Just because you see a blue eating something does not mean it killed it. They are VERY efficient carrion eaters. If something in my tank dies, a blue is usually on it in minutes.
Snails die for lots of reasons and if a blue is eating it, he is just doing what you bought him for - cleaning up.
I also keep about 2 extra shells for my hermits, but even when I did not they were fine.