Milter-greylist

I have one domain that gets enormous amounts of "undeliverable mail" 
notification messages due to joe jobs (see http://members.cox.net/joejob/)

Does milter-greylist handle null reverse-path messages like "normal" 
email? It seems, to me atleast, like a waste to store these in the 
database. They should of course be subject to the initial greylist 
period but why whitelist them?

Regards, Tony