If using get_the_terms, you can just do your if loop once for each taxonomy and then join them after the three loops.
Of course, it would probably be more efficient to use:
wp_get_post_terms( $post_id, $taxonomy, $args );
You could then do something like:
wp_get_post_terms( $post_id, array( 'resource_roles', 'resource_media', 'resource_theme' ) );
Which would pull all of the terms in one query.