I keep three in my heavily planted 75 gallon. Yes they do eat snails.

 

I have 4 or so in a pretty heavily planted tank. They do eat some snails, but not to the degree other loaches do.
Just make sure they have some good cover so they feel more secure. Plants will work, but they prefer something like a piece of driftwood they can get under.

 

i have two kuhli loaches in a 20G tank that is beginning to take shape. i haven't seen them put a dent in the snail population (never seen them eat one). they leave shrimp alone, too, provided the shrimp are big enuff not to be eaten.

re: environment, they need plenty of hiding spaces. they typically hide during the day and come out at nite.