Yes, there is evidence for that. But a few things:
1. Hypnotherapy is a broad term with little consensus among its practitioners on what exactly it is.
2. Many (probably the vast majority) of hypnotherapists aren't primarily treating pain-related problems
3. Even for pain, the studies are not of great quality. I'd love to see more studies of hypnosis vs. sham hypnosis
4. Perhaps most importantly, I still don't understand how hypnosis works. Are we saying that chronic pain goes away b/c I am able to suggest to you that the pain will go away. This to me sounds exactly the same as a placebo effect. Simply stated, what is the difference between placebo and hypnosis?
With the file drawer effect and enough low-quality studies, I can see why the evidence points to hypnosis being effective for chronic pain (especially this condition b/c it is so broad and amorphous). However, theoretically it doesn't make sense.
Note: this is not my area of expertise and I would love to be provided evidence to the contrary.