A few things come to mind:
1) As hard as it may be, and as frustrating as it cam be, you are
just now right about at 24 hours since you started experiencing the problem. At this point, filing "many" support tickets is probably not all that productive except to the degree that it provides additional information to the tech about specifics. Normally DreamHost is much faster, but they only represent that they will try to respond to support requests within 24 hours, so as difficult as it is, some patience is probably in order.
2) Even though I have no idea why this is the case, I have noticed anecdotally that the single most unpredictable experience I have had on DreamHost is the amount of time it takes to create and activate a new user and mailbox. I've had it happen almost instantly, and I have had it take over 24 hours on many occasions. I assume that the control panel collects the information for subsequent batch processing, and that some times that processing is faster than other times.
3) I have seen that not all aspects of email service "go live" at the same time. POP3 may often work before IMAP/webmail, and sometimes one will work when the other will not int he period immediateloy following creation.
3) While there is no indication of a spacy cluster problem, Tuesday is traditionally when DreamHost rolls out changes to their backend codebase. If you note yesterday's newsletter (it's already on the wiki if yours has not found it's way through the mail queue yet), there were some changes to the way email users/accounts were created. I have no way of knowing if any of this could have a bearing on any new email addresses that might have been in the queue to be created when the changes were rolled out. I suspect it is possible that some of them might have incompletely created as batches may have been interrupted. If this was the case, they may need some time to sort it.
I have no idea whether any of that has a bearing on your situation, but I think it might, and if that is the case, since you have already filed the support tickets, I don't know what else you can do at this point except to hope they can get it resolved as soon as possible.
One thing I know will not help, it being upset about it .. the stress is bad for you!
I really do hope they can get everything in order for you quickly.