I started in the aquarium hobby solely because I thought kuhliis were adorable and cool so those were some of the first fish I got before I got all addicted. Never kept them with my shrimp because I had other fish in the tank that would DEFINITELY have eaten them (Yo-yo loach, Gobies).
But from my experience I can definitely tell you that when I had my kuhliis they had absolutely NO interest in the snails in my tank...big, small, whatever. Frustration set in because I got bored of crushing snails and letting the other fish eat them (and I couldn't copper them out b/c I was thinking of adding shrimp) so I finally got one (1) small (tiny at the time) yo-yo and let him loose.
Not two days after I got the Yo-yo, I had no big snails (lots of empty shells and shell bits), and about three weeks later, no small snails. I did have one (1 still) very FAT HAPPY yo-yo loach.
Net net here though is anything that you introduce that will eat your snails will almost certainly go after your shrimp (unless you have very small snails that you have a fish that can only eat those and can't eat your shrimp (but even then, it would eat your shrimp babies).