Never, ever, skip the programming test. Many/most certifications will indicate technical competency of a skill, which is great, but not enough. Hopefully the certification is rigorous, but it would still be good to know that the candidate hasn't learnt their skill by rote.
You want to see that the candidate can actually work through a problem, that they have thinking skills, that they have learnt from experience (both their own and others), and that they know their own limitations. These are qualities that may not be evident from their certification.
Yes you can hire the person on a test, and keep them on probation until you validate their competency. But why put both of you through the stress of firing somebody (not to mention the cost of setting them up for day 1 of work) if you can avoid it with an extra 30-60 minutes work up front during the interview stage?
Yes and no. Yes, I do - but only for pure textbook questions. I assume the programmer knwos what the test certifies - and i will immediately termiante if significant omissions happen.