From what I've read I think I know already that the answer to this is "nope, not really", but I'll ask anyways. I've got a bunch of Linux servers that have been running for years, and I have no plans of rebuilding them from scratch, and I'd like to add an IDS to them. The tripwire documentation says that there's no way to ensure that the system hasn't already been compromised and therefore adding it will only help with future breaches. Fair enough.
But, if you wanted to anyways, would it be sufficient to scan the system using for example unhide, rkhunter, chkrootkit, and tiger first and then add an IDS? Or, would it be possible to create a virtual machine with the same package selection, add an IDS, build a configuration and database, and then copy those over to the production server?