The negotiation space is private to you, the other party, the mediator and the system administrator. No one else has the ability to view your conversation. With very limited exceptions, such as threatening harm to another person, all discussions are confidential and cannot be used in court.
There may be a time when you would like the mediator to know something that you don't want to share with the other party. In this case, the ODR site allows you to communicate privately with the mediator, who will keep this information confidential. You can have a private conversation with just the mediator by clicking on the "[your name] +Online Mediator" tab.