The install document says 100GB but is there a scaling/sizing document on the DB sizing?
I don't believe so, at least I haven't seen VMware produce a publicly-accessible one.
The "Architecting a vCloud" whitepaper also cites 100 GB of storage for Oracle DB: http://www.vmware.com/technical-resources/products/vcloud-director.html
In practice, if you're just trying it out or don't expect to set up a production cloud using VCD you can probably get away with an order of magnitude less storage.
I saw the 100GB on the documentation earlier. I wanted to understand the numbers for production deployment so that we are provisioning the Oracle server properly. I assume no recommended numbers for vChargeBack as well?