Apparently, the $SIG{__DIE__} causes the program to exit with a status of zero.

No, it doesn't

>type script.pl
#!/usr/bin/perl

$SIG{__DIE__} = sub { die @_ };
no_such_sub();

>echo %ERRORLEVEL%
0

>perl script.pl
Undefined subroutine &main::no_such_sub called at script.pl line 4.

>echo %ERRORLEVEL%
255
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It's whatever prints '1..1' that causes the program to exist with a status of zero.

>type script.pl
#!/usr/bin/perl

use strict;
use warnings;
use Test::More 'no_plan';

ok 1, 'this works';
$SIG{__DIE__} = sub { die @_ };
ok no_such_sub(), '... no such sub';

>echo %ERRORLEVEL%
0

>perl script.pl
ok 1 - this works
Undefined subroutine &main::no_such_sub called at script.pl line 9.
1..1

>echo %ERRORLEVEL%
0
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You'll get very similar results if you take out the $SIG{__DIE__}. That's why you should use a plan.