#!/usr/bin/perl
use warnings;
use strict;

use Data::Dumper;

my %hash1 = (key1 => [qw(val1 val2)],
             key2 => ['val3'],
             );
my %hash2 = (val1 => [qw(val5 val6 val7)],
             val2 => [qw(val8 val9)],
             val3 => ['val3'],
            );
print Dumper { map { $_ => [ map @{ $hash2{$_} } ,
                                 @{ $hash1{$_} }
                           ]
             } keys %hash1 };