I wouldn't be confident that a designer who can't code in HTML/CSS would understand the restrictions of the medium. I've seen a lot of great "website designs" done in Photoshop that wouldn't make terrible websites due to load speed, structure, or other unconsidered elements.

I'd say the answer somewhat depends on the specific candidates and your budget. There's rockstar designer/coders out there and there's good designers and coders.

Try hiring a front-end coder who does their mockups in Photoshop. That could narrow out serial wireframers (wireframes are good, just not when used to build a design) and help you find someone who's the best of both worlds.

Maybe you're also getting a lot of non-coders because of the location you listed the job as well. Try posting a job here on HN, asking for a referral to a good designer or a more established "design+coding" marketplace.