It's not really a hiccup because it wouldn't work anywhere else in the same situation either. That's why I pointed out that because of Dreamhost's size, the chances increase, only because of the numbers.
The other thing to keep in mind about "proof of purchase" is that if it can be duplicated on a computer, it likely won't be enough. If you have WHOIS privacy enabled, that will likely slow the process down as well.
Everything you said can be checked out through the WHOIS history, which I'm sure they'll look at -- but I still wouldn't expect them to just unplug anything until they've made contact with the current customer that has it in their account. You have to picture how you would want it to work if you were on the other end.
What you could do, that might help... or at least won't hurt since you can't do anything with it now, would be to redirect it somewhere else to show them the other customer has no control. Do you have another account somewhere, or a friend that does? If so, you could add it there and just throw up a page that says, "See, Dreamhost? I told you it was mine!"
If not, you could redirect it to your Dreamhost affiliate link and let them check the headers. Maybe you'll even luck out and get a few sign-ups in the process.
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