The behaviors you describe suggest that it is quite possible that your son has ADHD as a co-existing condition. Your suggestion to have the teacher make records of his behavior is a very good idea, but since she seems to lack objectivity at this point, I would have some other professional do the observations and record the behavior. I would suggest the school psychologist or social worker, or better yet, an independent psychologist with expertise in both CP and ADHD -- perhaps from a local children's hospital. The school should pay for this consultation in the interest of objective data collection. This observation should be part of a diagnostic process, which uses information from you, the teachers, and from the observations. This is a complex situation and many teachers are not well versed in how CP manifests itself in the classroom. Therefore, this must be a team approach involving appropriately trained professionals. You might want to contact the local branch of United Cerebral Palsy and ask them for a consultation, IF they have someone on board who knows about the education of children with mild CP. (They often tend to work with more seriously involved adults.)
You are right that there seems to be an overuse and too often a misuse of the ADHD label. However, the behaviors that the teacher describes may best be treated using behavioral approaches that have been successful with children with ADHD, even though you may not be able to get a clear-cut diagnosis. A classroom with structure, firm expectations, behavior modification strategies, and a warm, empathic teacher can do wonders for a child like this.