Set Job Tags taxonomy type as hierarchical (untested) for WP Job Manager Tags

functions.php

<?php

// Requires WordPress 4.4+
add_filter( 'register_taxonomy_args', 'smyles_set_job_tags_hierarchical', 10, 3);

function smyles_set_job_tags_hierarchical( $args, $taxonomy, $object_type ){

	if( $taxonomy === 'job_listing_tag' ){
		$args['hierarchical'] = true;
	}
	
	return $args;
}

Works perfectly.