This thread can be resolved.
Here is what I did to fix it and this is what I would expect to see in future forum threads:
Generate a self signed certificate on the RHDS Server. Import the certificate into Zimbra using the following command:
sudo /opt/zimbra/java/bin/keytool -import -alias <alias> -keystore /opt/zimbra/java/jre/lib/security/cacerts -storepass changeit -file <certfile>
In the previous versions of Zimbra it required the user to restart Tomcat, but I believe Tomcat has been replaced with mailboxd. So I did the following as Zimbra user:
zmmailboxdctl stop
zmmailboxdctl start
zmcontrol stop
zmcontrol start
Just a side note, the certfile that is used to import can be of any file type. I found it easy to just copy the cert file into a text file and import it in.
It may not be necessary, but I imported in the RHDS Admin Server Cert, the RHDS Directory Server Cert and the CA Cert.