domain mapping does not seem to work or apply


I have successfully installed domain mapping plugin for my multisite But when I tried to map one subdomain to it does not work.

On under Tools > Domain Mapping I'm entering "" and clicking Add button. The page refreshes but nothing seems to happen was not added.
I have already added a custom DNS A record and have as its value.

However there is also a Non-editable DreamHost DNS record and the A record has the value

Does this mean I need a dedicated IP from my host? which is Dreamhost. I have VPS with them.
I checked the IP and its not resolving to my WPMU site.

Thanks for your help.