Try setting up "dummy" tree quotas to start. These are quotas with no limits, but it forces ONTAP to trace the space usage which can then allow DFM to run reports on their size.
In /etc/quotas put a dash ("-") where the size limits should be, just like most people do for file limits. Then initialize the quotas. When you're done, the quota report command will show you how much space you have in your qtrees on which you set up your dummy quotas, but won't put a cap on them. Now, DFM should be able to use that to figure out sizes and ulitmatley chargebacks.
Hope this helps.
