It seem ns1 is working must fine now. It's possible there was a temporary glitch or that the server was simply overloaded. But the thing with this system is that it's not a big deal if one name server doesn't respond - that's why there's three of them. Each name server, ns1.dreamhost.com ns2 and ns3 all hold exactly the same data - but if one's busy or not working there's 2 more.
You can test if for your self, http://www.dnsstuff.com/ has great free tools to help you check on this sort of stuff. Just scroll down to get their free tools.
I was also able to do a reverse DNS lookup through that site for one of my Domain's IPs. It correctly found traced it back to Dreamhost and the server I'm hosted on. Does that answer your question?
art.googlies.net - personal website