The longer you have the lion, the greater the risk could be for something like a peppermint shrimp. How much of a risk will depend on many different factors like hiding places, how well the shrimp is fed, how well the lion is fed, personality of the lion, exposure to food item, size differential at any given time. Even if the tank is a little warmer in the summer, that will make them a little hungrier, and the shrimp a little tastier looking. Hey, when a plane crashed in the Andes, most of that rugby team choose to eat friends verses eating nothing..... don't underestimate hunger.

I have a mombasae lion, that has no idea what live food is and the shrimp would climb all over him while he waited for me to feed him some cod. Then I have a barberi lion that would eat his own self, if he could figure out how to do it.
Personality can have a lot to do with tankmate compatibility. You also have to remember, personalities can change as they grow older, as social order changes or environment changes. I had a pair of fuzzy lions that were just awesome. When they started breeding, they started being aggressive to EVERYONE. The whole tank dynamic totally changed at that time.
Snail and hermits are safe. When crabs are smaller, they can be snack size. But if they live until they are larger, they are generally safe for dwarfs. Shrimp are, generally, the one most commonly at risk.