several scripts (e.g. tetex and tmpwatch) are placed in /etc/cron.daily but I cannot find any evidence that they ever get executed. the format of /etc/crontab and /etc/cron.d/* is not documented. there is just a dead reference to crontab(5) in cron(8) Also I want to say that I would prefer logging to be done via syslog.
Both tetex.cron and tmpwatch scripts use tmpwatch(8) which does not log its actions, so no evidence will be left around. man -S 5 crontab is your friend. /usr/bin/run-parts is used by the system crontab, /etc/crontab, to run the scripts in /etc/cron.daily etc. Your suggestion about logging to syslogd will be passed on.