Template is usually an HTML document, not a Perl source code, so Perl escapes don't work there. HTML entities do, though. You can always pass a constant from Perl to a template, too.

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

use open OUT => ':encoding(UTF-8)', ':std';

use Template;

'Template'->new->process(\'SUMMARY:[% chr(128054) %] [% dog %] &#x1f43
+6; Dog Face Test',
                         {dog => "\x{1f436}",
                          chr => \&CORE::chr});
[download]

Update: Added the chr sub.