Anyway to hide a Category in the Categories section when adding/editing a post in WP Admin?

a simple way to hide it would be to find the ID of the category li and use css to set it to display:none.

function hide_the_category(){
    ?>
    <style type="text/css">
        li#category-4{
            display:none;
        }
    </style>
    <?php
}
add_action( "admin_head", "hide_the_category" );