Ok this is weird. There is no text below 'domain management' and definitely not any green circle with a plus in it anywhere on that page. (yes I'm on the right page, not the registration one)
However, I am able to use the second link you provided to get to the add page, so I guess that solves my problem. Hooray!
This of course begs the question, why would that link not be there? Is there some kind of account setting for that? Or should I open a support ticket with DH to get it resolved?
Thanks for the responses!!