Code example for a cronjob to perform every hour.
0 * * * * su - username -c '/home/username/gameserver monitor' > /dev/null 2>&1
Your cronjob looks to be correct.
./csgoserver u and ./csgoserver update are the same, one is a shortned version. Check ./csgoserver for the detailed output of all the commands.
NOTICE: That the above has to be performed under the ROOT cronjob. If you want to do a cronjob under the user profile, it would look like this:
0 * * * * /home/username/gameserver monitor > /dev/null 2>&1