During preparation to Exchange 2010 migration to Office 365, I have come across a post that says
"Apparently the dirsync tool by default WILL NOT SYNC EMPTY distribution groups.... If your distribution group is empty it will be filtered out and wont sync. (you could manually join it with the joiner tool and after that it will sync)"
***Is that the case about empty distribution groups?
Also, the author is saying: "Also on syncing contacts from an AD OU make sure you have NO "-" in the OU name as having a "-" in the OU name will prevent the default settings to sync contact from it."
***I cannot confirm it anywhere else, starting with http://technet.microsoft.com/en-us/library/hh852478.aspx
Prepare to provision users through directory synchronization to Office 365