I am not sure about ArcSight but most SIEM programs have programs will have modules that will "equalize" to the database many syslog formats per device manufacturer. Our SIEM product has what are called DSM modules that take many different syslog formats from hundreds of vendors so that the data presented is equal in the database. Out SIEM has a DSM module specific for XOS and EOS boxes, please check with HP on what is available in your circumstance. I tried checking the HP Enterprise site but was unable to search their support database.