Hopefully one of the folks that works in that support realm (Security Response/IQ services) will be able to respond to this; it is not an internal function of the SMG appliance.
As to the SMG appliance though, reverse DNS was only recently implemented as an actionable check (version 9.5). Prior versions would only alert on reverse DNS failures, primarily because DNS implementations have historically had a varying degree of proper configurations. However, even though the current version of the SMG appliance does DNS validation, it is not on by default. And when it is enabled, it does very specific checks directly against the DNS source and does not access a global reputation for for these checks.
If you are experiencing issues with DNS validation on the SMG appliance, it would probably be best to open a support ticket for investigation into functionality. I have not seen any situations where these checks are failing due to functionality, and not due to DNS.