#!/usr/bin/env perl

use strict;
use warnings;

use Data::Dump;

my $h1 = {locset => [409], status => [501, 137]};
my $h2 = {status  => [137, 124], locset => [405, 409], class => [0]};

my %seen = map { $_ => { map { $_ => 1 } @{$h1->{$_}} } } keys %$h1;

my $x = $h1;

for my $key (keys %$h2) {
    if (exists $seen{$key}) {
        push @{$x->{$key}}, grep { ! $seen{$key}{$_} } @{$h2->{$key}};
    }
    else {
        $x->{$key} = $h2->{$key};
    }
}

dd $x;

##</code><code>##

{ class => [0], locset => [409, 405], status => [501, 137, 124] }