CLI errors don't log to Apache.. db though, good thinking.
Could also be a difference of config between Apache and command line php.ini's, on my boxes they are different, but not fatal error different. You able to run other cli php scripts?
But if you're not fetching or sending email, then what do you need cron for?
Could you share the actual cron line?
They user$ bit at the end makes me think you're passing a parameter to the script, or running as nobody but requiring a specific user, or trying to run as www-data/apache etc, however that user can't run scripts (no shell etc in /etc/login).