Be extra careful, depending on whom you’re blowing the whistle.
I have privately registered domains through GoDaddy.com (who is affiliated with Domains By Proxy), and have been happy with it because it does rebuf a whois query, but I think the veil of privacy is relatively easy to have pierced.
If you read the proxy agreement at DomainsByProxy, you can interpret that a simple subpoena can obtain the otherwise anonymous information.
So if you’re going after someone with deep enough pockets to have legal representation that can press the argument that you are defaming/slandering/etc. them, they could sue to get the data. I actually have a friend that was on the phone with a private registrar once and threatened legal action and got the information.
My guess is that Dreamhost would also surrender any information if they were served.
You might want to consult with an attorney if you are really worried about what legal ground you’ll be standing on (what you’re planning on saying, how you’re planning on saying it, and against whom you’re going to say it).