The firepower was not resolving the DC’s host name. I'm not having trouble accessing the FDM from any interface.
I had to create a new DNS Group that included the DC’s IP in addition to the Cisco Umbrella DNS servers.
Once the Firepower is connected to the production LAN I will have to add another network DNS server to the group. This is not ideal.
What I was trying to accomplish is to create one DNS group for inside interface A and another DNS Group for inside interface B.