Well considering we wouldn't act on a report unless the proof provided was sufficient enough to actually show that the player has been breaking rules, I think the player wouldn't need to have to respond to it.
In the other situations where a report would need to be investigated I'm sure the moderator who looked at the report would look into the matter first, perhaps question the player if necessary, and any other precautions to make sure that the report is valid before actually moving to ban or warn the player reported.
The time for a player to dispute the report would come if the moderator found that the player was to be given punishment (Ie suspension of account or ban). In which case they would need to then explain why they took the action of breaking the rules, request to be unbanned if so, or request to be informed of why they were banned so they would further know.
Since we wouldn't act on a report such as "X was griefing", and X was not griefing and there was no proof at all provided by the reporter, X would not need to worry that they were reported at all. With this new privacy policy someone wouldn't have to feel upset that someone would falsely report them, or a reporter wouldn't have to be upset that they're reporting a friend when the friend could see it.