Ha ha ha. I'm both "chilled" and "relaxed"; you misunderstood the whole point of atropos7's post ... I don't care what you do, seriously, but I'd hate to see your good intentions result in the loss of your account.
His point was to warn you about the risks to your account if you proceed with what you appear to be assuming is going to be "ok", and from your last post it's apparent that is was a warranted warning.
You have either not understood what you have read, or are ignoring the risk to your account, if you think that any supposed compliance with the CAN-SPAM act, or your own determination of what constitutes an "opt-in," is going to make you compliant with DreamHost's Anti-Spam policies. You can be 100% "CAN-SPAM compliant", as are many spammers, and still place your account at risk for not being compliant with DreamHost's Anti-Spam policy. I'm not saying you are a spammer, but that's a minor distinction if you don't comply with the spam related aspects of the TOS, because you can end up being treated as one.
That's great, and I'm sure that most, if not all, of those you will mail to will be happy to get the mail, but that is not the issue with Anti-spam policy compliance. You may function for years in a "non-compliant mode" and have no problems, but a very few (possibly even a single one) "complaint" (someone who forgot years ago that they signed up, or someone who doesn't recognize the mailing for what it is, etc.) can trigger a review of your compliance procedures, and you will be found lacking. I have clients that can testify to that reality.
That's all fine and good, and it may indeed be reasonable, but it is not compliant with the DreamHost (and many other companies') Terms of Service or their Anti-Spam Policies.
1) Unless they have "confirmed opt-in" via an electronic process, and you can provide the date, time, and IP address from which they did so, you are not compliant.
2) A prior relationship is completely irrelevant to the TOS or the Anti-spam policy (and is one of the "loopholes" in CAN-SPAM that makes CAN-SPAM more of a spammers' justification mechanism than a legitimate spam deterrent).
3) It's great that you take seriously your responsibility to keep your list clean and current, but again, it is irrelevant when it comes to complying with the TOS or the Anti-spam policy.
You really should take the time to read the Anti-spam policy again; possibly you will find the clarifications and the "Q and A" in the information at the DreamHost Abuse Center sections on the subject to be enlightening, as they address some of the statements you have made in this last post.
There are also many threads that address this, and your particular position on some of it, in these forums. The search function will point you to many of them (here is one you might find enlightening - then again, maybe not!)
There is no "import" facility to do that for you provided by DreamHost, though it should be a trivial data-processing task to manipulate that CSV list into a text-file format that could be "cut-n-pasted" into the "Edit Subscriber List" textarea of the announcement list management form in the web control panel.
There is more information about importing subscribers in the DreamHost wiki (which again warns you about being policy compliant with your imports), and the following section that describes "exporting" may be helpful (you could basically "reverse" that procedure to "import" your CSV list).
Edited: Oops! my original response about the "import" referred to my previouspost in another thread, not this one ... Mea Culpa!