First: reflect on the fact that DevOps is a cultural shift about collaboration. Do you want to hire a DevOps person, or encourage people to collaborate?
Second: make them write fizzbuzz. In front of you. In any language they care to use. Can they make it work? Can they discuss how they might have done it differently?
Third: ask them to write some Puppet, Chef, or Cfengine code, to solve a specific and contrived problem. Don’t make them solve a real-world problem yet, as you want them to demonstrate their skills in infrastructure-as-code. Discuss their solution as above.
If you’re happy at this point, you can continue a normal hiring process.