Hi, the "nginx.service" file shipped with systemd rpm's both in nginx's stable repository and epel for CentOS7 / RHEL7 do not perform a "configtest" when "systemctl reload nginx" is issued.
So if there is an error in the configuration file nginx is killed but not started due to the faulty configuration.
It's possible to mitigate this in the nginx.service file by having two "ExecReload" commands on separate lines like so:
# grep ExecReload /usr/lib/systemd/system/nginx.service
ExecReload=/usr/sbin/nginx -t
ExecReload=/bin/kill -s HUP $MAINPID

This way if the configtest in the first line fails nginx is never killed, the command does not print any output but that is a systemd issue so I think unavoidable.

I can't guarantee that this is a supported way to do this but it works for me at least :)