Yes, that's correct and the drop down doesn't give openDNS as an option. However, I may be wrong but I understood that the SH2 would allow you to use a DNS so that the dynamic IP address they provide could be changed to a domain 'name' so that access to my home network would be not be effected by periodic new IP addresses.
The use-case you outline is (as others have pointed out) called Dynamic DNS, or DDNS. OpenDNS does not, to my knowledge, provide a DDNS solution, although they do provide a mechanism to inform DDNS providers when your dynamic IP address changes. This, however, is unlikely to be of any use to you as the SH2 doesn't support it (as you have seen).
If you want to access your home network using a consistent domain name, and you want to keep using the SH2, then you would need to sign up for DDNS service with one of the providers the SH2 supports. These will provide you with a domain name which maps to your IP address, with the SH2 updating them when your IP address changes.
