OK, Maybe it's the DB admin in me but why not this:

my %Emails = ( 'Name 1' => 'Some1@somewhere.com',
  'Name 2' => 'Some2@whereelse.com',
  'Name 3' => 'Some3@nowhere.com',
  'Name 4' => 'Some4@someelse.com',
  'Category1' => [ 'Name 1', 'Name 2' ],
  'Category2' => [ 'Name 2', 'Name 3', 'Name 4'],
);

sub GetEMailFor {
  my %names = ();
  foreach my $request ( @_ ) {
    if (ref ($Emails{$request}) eq 'ARRAY') {
      foreach my $em (@{$Emails{$request}}) {
        $names{$em}=1;
      }
    } else {
      $names{$request}=1;
    }
  }
  return join ',', map($Emails{$_}, keys %names);
}

print (GetEMailFor('Name 1', "Category2") ."\n");
[download]

Actually tested... and I leave the recursion that would allow categories to contain other category references as an exercise for the reader.

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