What is the url to the site that is down?
If you have already sent the ticket, at this point you just have to wait for a response (though there are some other things you could be checking yourself).
Sending multiple "priority 1" ticket within 1.5 hours won't help - it just adds another ticket to the support queue.
You can always try the contact form at http://dreamhost.com/.contact.cgi, but that is not as good a way as submitting a ticket (which you have already done).
If that delay is "absolutely unacceptable", you are probably not going to be happy with DreamHost. While most of my ticket are answered very quickly (usually within minutes, sometimes within hours, almost always withing 24 hours), 1.5 hours is not an unreasonable amount of time for an email response.
Good luck - I hope they get you sorted soon.