Do the same thing, but have the account owner make the contact, and pick the "I forgot my password" option in the dropdown box. The password needed is the one for the dreamhost panel, once that has been established you can change or lookup passwords using the panel. Some dreamhost passwords (such as mysql user passwords) can be looked up, others will have to be changed because dreamhost doesn't store them in a recoverable form.
The key thing, cut out the middle man, that's you. Dreamhost can't give you access. After access has been established your customer/friend whoever can choose to give you the password so that you can further assist him with other passwords connected to the account, but if you are contacting the security team on behalf of the customer there is really nothing they can do other that write back and tell you to have to customer make contact.