Fortunately, I only received one piece of spam through the email address I used for the DH account. Strangely enough, it was trying to sell me web hosting. A friend who also signed on with DH received exactly the same email.
I am pretty sure you are correct and the name/email address is being lifted from the whois results for the domain.
You can change the whois information in the control panel. Goto Domains -> Registrations, tick the checkbox next to the domain(s) you want to change, then click Modify Checked
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