Well, here's the way I see it in my panel.
I host a few clients with google mail, and in my panel under "Manage Email" at the bottom of that page there is a section that says.. "Gmail-Managed Domains" which includes the domains that are hosted by gmail.
If dreamhost is forwarding mail, you can probably be sure that it's not setup properly to allow gmail to handle the email at all.
To make sure you've done this:
Domains > Manage Domains.
Select the domain that is in question. In the "Web Hosting" section click the "Edit" button.
I have a domain example.com that is "Fully Hosted" by Dreamhost, except the email. So in the "Fully Hosted" area, I have setup the directory that I want the domain to render /example/
Then a few sections down from that, I have "checked" the box for.. "Google Apps" and/or "GMail".
Make sure that box is checked by gmail. Because once you do that, dreamhost will change your DNS records to reflext an MX (Mail Exchange) record that will send ALL of your email to google (which shouldn't allow dreamhost to forward the mail sent to a specific address, that would need to be done inside the gmail control panel).
It will also allow you to go to http://mail.example.com which will take you to the gmail login
I really hope this helps you, and if you need any thing further, feel free to contact me off the board, and I can walk you through some things via IM
qbx (@) wiredinter (.) net