Sometimes. Better to try simple measures first, ie restricting fluids, lifting to toilet at night, bedwetting alarm or medication.
Yes. Actually, I do not have experience with this in children but was very successful in treating an adult patient with bed wetting. Once again, the hypnosis is a tool and one has to decide how to approach the problem using that tool. The fact that one has not done a scientific study, does not necessarily mean that the treatment does not work.
No convincing data. Bladder alarm has been the most effective treatment for night time bed wetting.