One possibility is to have all replies sent to another mail box and from there monitor the Out of Office replies. It is manual but stops the potential for mail loops.
One other option is to look at the Email Commands and see if there is one that could be used with the out of office message. I dont think there is one unless youjust want the history lines updated and not a diary style text field updated.
My understanding (with earlier service packs at least) is that the Out of office reply will be sent to the From address and not the Reply-to address of the incoming message. Typically it is best practice to have the from address and reply to address different and only accept incoming email using the reply to address not the from address - to avoid email loops from Out of Office Assistants etc.
And yes the from address could be an exchange public folder or mailbox that you monitor for Out of office assistant messages.