It sounds like your account with DH is minimal, i.e. it allows domain registrations but provides no hosting.
That would be fine, if DH allowed a registration-only account to edit the DNS zone files for domains that it has registered.
There has been conflicting advice about whether DH provides this service.
The wiki suggests yes (http://wiki.dreamhost.com/Custom_DNS) "Note that it is possible to use the DNS Only hosting service in our system without an active hosting plan, however this only works for domains that are registered in our system", but more than one thread here has said no.
The wiki could be wrong, or at least confusingly written.
Anyway, if DH doesn't provide this, and if this is what you want to do, then you could transfer your registration to another registrar that does allow DNS edits for registration-only accounts. You might have to pay $12 instead of $10 for a registration.
(Then, to validate with google, you would choose one of their alternative validation methods which do not involve uploading an HTML file, but which involve editing the DNS instead.)