Forwarding in Gmail is left to the owner of the email address, not the administrator.
Setup Dreamhost to manage mail on the domains that you require forwarded individual emails.
Panel > Mail > Custom MX
Gmail domains will have "uses Gmail" next to them.
Click Edit and on the next page is a button that returns the MX to Dreamhost.
After that it's a simple case of going to Panel > Mail > Manage Email again, clicking the Create New Email Address button up top, and filling out the Forward-Only Email section on the following page.
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