Ok so I only have EL systems to hand but I asked a friend who as a Debian 8 system and the answer is broadly the same.
For Debian using cron (substitute crond for EL)
systemctl status cron
systemctl status cron
cron.service - Regular background program processing daemon
Loaded: loaded (/lib/systemd/system/cron.service; enabled)
Active: active (running) since Mon 2015-11-02 21:13:22 CET; 1 months 0 days ago
Docs: man:cron(8)
Main PID: 983 (cron)
CGroup: /system.slice/cron.service
983 /usr/sbin/cron -f
If you then look at the contents of /lib/systemd/system/cron.service
[Unit]
Description=Regular background program processing daemon
Documentation=man:cron(8)
[Service]
EnvironmentFile=-/etc/default/cron
ExecStart=/usr/sbin/cron -f $EXTRA_OPTS
IgnoreSIGPIPE=false
KillMode=process
[Install]
WantedBy=multi-user.target
You can see that it loads an environment file /etc/default/cron
amd from that file it uses $EXTRA_OPTS
If your cron daemon supports it you can provide an option to change the logging verbosity there
EXTRA_OPTS="-L 0"
The man page for your distro's cron(d)(8) should tell you what logging options you have.