Certainly check with the RedSky folks. You can't be the first person to ask this question.
As I understand it, the CER server will have an ongoing encrypted SIP Trunk to RedSky for information updates/exchanges. It may be that you will have to change a firewall rule or set up an ALG rule to allow CER to connect to RedSky anyway. So absolutely check with RedSky. They are nice folks.
Maren