1. I am concerned about recent behavior, including last night, where my son is being used as a tool instead of my ex-wife communicating with me. He also called me last night attacking me for going to court and asking for sole custody. The court specifically ordered that the parents shall not discuss court proceedings or show court papers to the child and I have not said this so I know that my ex-wife must have.
If you believe your wife has violated the court order, there are options. For example, a motion for contempt is commonly used by parents to punish misconduct of this kind, when the other parent is intentionally and willfully acting contrary to the court's instructions. Bringing such action to the court's attention alerts not only the judge but also any evaluators as well about the behavior.
2. Is there any process whereby I can provide my concerns to the interviewer before she interviews our son? Or, would the interviewer likely misread my attempt to inform her as an attempt to manipulate the process?
Without knowing the particulars of the case or the reputation of the evaluator, it is truly impossible to say. In some cases, they will want as much information as possible and tell you so, their requests for insight are on-going. They take the information and assess it along with whatever additional information they receive from the children. On the other hand, evaluators that are particularly biased in favor of one gender or the other (e.g. the mother, for example) may take whatever information is provided and use it against the other parent. I've seen both happen. As noted above, however, the evaluator is able to review the paperwork that has been filed in the legal proceeding, including any allegations of contempt, and so can become aware of the behavior indirectly. Complaints of misconduct can also be brought to the evaluator's attention during any interviews with the parents, or via communications with the attorney or agent representing the children (if any).