It's ok, but so far eviolite dusclops is the best eviolite mixed wall. Shelmet has some pretty decent defenses and could have the potential as a talented wall, hope you make good use of him! The moveset I like is:
Shelmet/nature:calm(+special defense, -attack)trait:hydration/item:eviolite
-yawn(force out a switch)
-toxic(drain their energy)
-giga drain/bug buzz(only if you EV train his special attack to the maximum)
I actually used this guy a couple of times, and he turned out to be a decent wall. It would be best to use him on a rain dance team to make use of his ability.