Centralizing logging from Apache may not be a good fit for syslog-ng, I'd instead consider aggressively rotating logs on each server where the websites are hosted, then use a file-based transfer mechanism.
______________________________________________________________________________
Member info: https://lists.balabit.hu/mailman/listinfo/syslog-ng
Documentation: http://www.balabit.com/support/documentation/?product=syslog-ng
FAQ: http://www.balabit.com/wiki/syslog-ng-faq