I am not sure that thread is the one you intended to link to.
I think the thread linked below is probably more related to the OP's issue.
Note: In this thread 'clientname.com' is used to refer to the parent domain, which is not hosted at DreamHost, while 'clientarea.clientname.com' refers to the sub-domain, which is to be hosted at DreamHost.
Also, to the OP; I notice that you said that the domain owner has created a DNS record pointing to your DreamHost server IP address. This IP address is unlikely to be the one you need. At DreamHost, IP addresses are assigned from a pool of addresses and the domains and sub-domains that you add to the system are not guaranteed to share the same IP address. The thread linked above shows how to obtain the correct IP address for your sub-domain.
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