I've observed that drush crashes with a segfault if the xmlsitemap cron function is run. Either as part of the cron hook or directly through eval.

The map itself seems to be build correctly.

PHP 5.3.8 (cli) (built: Oct 21 2011 12:19:47)
Zend Engine v2.3.0, Copyright (c) 1998-2011 Zend Technologies

It is potentially related to the # of files ( > 150).