Can a page and a category have the same ID-nr ???

My question:
Can it happen in wordpress that pages and categories have the same id, lets say category id = 1 and page id = 1.
Are id-s unique to pages, categories, posts?

In case I want to show both pages and categories in navigation and use the same exclude textfield for both.
eg code bellow

<?php
$exclude_id = get_option('wptube_nav_exclude');
if (get_option('wptube_cat_menu') == "Categories") {
wp_list_categories('title_li=0&orderby=name&show_count=0&exclude='.$exclude_id.'');
} else if (get_option('wptube_cat_menu') == "Pages") {
wp_list_pages('title_li=0&sort_column=menu_order&exclude='.$exclude_id.'');
} else { wp_list_categories('title_li=0&orderby=name&show_count=0&exclude='.$exclude_id.'');
wp_list_pages('title_li=0&sort_column=menu_order&exclude='.$exclude_id.'');	}
?>