How to add an error or notification to an activity?

With enough digging I figured it out. First off you must save your error message to as activity meta data like so:

public function send_team_notification($activity) {
    $message = $this->send_custom_notification($activity->content);
    if(is_wp_error($message)){
        bp_activity_update_meta( $activity->id, 'custom_error', $message );
    }
}

This will appear in the database under the wp_bp_activity_meta table like so:

From there you can either manually update your theme template file, buddypress\activity\entry.php otherwise I chose to hook into the bp_activity_entry_meta action like so:

add_action('bp_activity_entry_meta', array( $this, 'add_activity_error') );
function add_activity_error(){
    $error = bp_activity_get_meta(bp_get_activity_id(), 'custom_error');
    _e('<div><p class="error">'.$error->get_error_message('error-code').'</p></div>');
}

Hope that helps!