Right now we don't have any way for customers to set up reverse DNS records. The primary reason for this is security. If someone had a reverse DNS entry for an IP and then deallocated from their DreamCompute tenant, that IP could later be assigned to another tenant.
We are following the OpenStack Designate project for automated DNS management that would help resolve this for DreamCompute. It's not quite ready for our needs yet but we're keeping an eye on it.