For the diamonds 0.5ct and larger used in their engagement ring collection, they come with a diamond certificate by RJC. That's a theory party gemologist that also certifies and audits their manufacturing process.
If you need certification for larger stones like the colored gemstones or opal stones often used in custom jewelry, you'd have to request one and pay an additional fee before the stone is set on the ring. Once the stone is set, you can't get a certification.