Do you know any reason why ArcSight ESM does not support the Cisco MARS? Right now, all my firwalls send the syslog feeds into Cisco MARS and I'm trying to set the Cisco MARS to send thoes raw feeds data to ArcSight local connector but I just found out that ArcSight does not support the Cisco MARS. Thanks in ADV for any info reading this subject.
Starting in 4.x, MARS can forward events to another remote syslog listener. ArcSight has a syslog connector. So you ought to be able to forward events from MARS to ArcSight via syslog assuming MARS doesn't change the format of the log events too much. Even if MARS does mangle the event format, ArcSight will still receive them, but then most or all of the event will be parsed into the CEF Name field and categorization and prioritization won't be accurate.
If you are unable to upgrade your MARS appliance to 4.31 or later (I think that's the rev you need), another option would be to use a syslog-ng server out front. It supports forwarding events by source to other syslog servers. You could use this to send the stuff you want in ESM to ArcSight's syslog Connector and the stuff you want in MARS to MARS.
Or, you could do the environmentally conscious thing and unplug then recycle your MARS appliance. ;-)