How to create a discussion post when a custom post is created?

Yes. It is possible publish_report action triggered whenever a report is published, or if it is edited and the status is changed to publish.
You have to done some error hadling.

function create_discussion_post( $ID, $post ) {
    //Write a code to create a discussion post.
}
add_action( 'publish_report', 'create_discussion_post');