use List::MoreUtils qw(first_index);

my @all;
my @data2_acc_list;

push @data2_acc_list, $data2->[$_]{ACC} for 0..$#$data2;

for (0..$#$data1){
    my $acc = $data1->[$_]{ACC};
    my $index = first_index { /$acc/ } @data2_acc_list;
    if ($index >= 0){
        push @all, { %{ $data1->[$_] }, %{ $data2->[$index] } };
    }
}

print Dumper \@all;