A similar question was asked recently: SysLog
bkyle suggested using a registry key to include more hosts in the daily report. This maxes out at 999 hosts so it doesn't work for us. Our default rule includes an action to log to a file. When configuring this action we use the 'AutoSplit' value to use the hostname as the log file name(C:\logs\hostslogs\%Hostname.txt). The hostlogs directory will then have a file for every host. From there you could do something like 'dir > hostlist.txt and use the text file.
Are you trying to detemine hosts that stopped sending or hosts that need to be configured to send to the syslog server?