domain mapping does not seem to work or apply

Hi,

I have successfully installed domain mapping plugin for my multisite http://www.iwebsite.ph. But when I tried to map one subdomain site1.iwebsite.ph to workimprovements.com it does not work.

On site1.iwebsite.ph under Tools > Domain Mapping I'm entering "workimprovements.com" and clicking Add button. The page refreshes but nothing seems to happen workimprovements.com was not added.
I have already added a custom DNS A record and have 173.236.148.220 as its value.

However there is also a Non-editable DreamHost DNS record and the A record has the value 69.163.193.118

Does this mean I need a dedicated IP from my host? which is Dreamhost. I have VPS with them.
I checked the IP 173.236.148.220 and its not resolving to my WPMU site.

Thanks for your help.