You certainly can get function return values back in perl. You can also get output arguments back in procedures. I do this all the time with DBD::Oracle.

use DBI;
use strict;
my $h = DBI->connect('dbi:Oracle:xxx','xxx','xxx');
eval {$h->do(q{drop function fred});};
my $sql = <<'EOT';
create function fred(a integer) return integer as
begin
  return (a + 1);
end;
EOT

$h->do($sql);
my $s = $h->prepare(q{begin ? := fred(?); end;});
$s->bind_param(2, 1);
my $res;
$s->bind_param_inout(1, \$res, 100);
$s->execute;
print "fred=$res\n";
[download]

outputs fred=2