If I unintentionally ignored a prominent member of a forum, would they be notified or informed about being ignored?
There is no such notification when a member ignored another member and you don't have to worry that if you ignore a forum staff, there will be notification which can stimulate that staff to chase you and find your rule violation to ban you. Just kidding but it's an example.
You are free to ignore any member, prominent or not.
From your side, after ignore a user, you can click on UnIgnore anytime to resume normal view.