I'm not having any issues when I test it out. I'm assuming you're uploading through the DreamHost control panel.
If you're not uploading via the control panel, make sure you've got the correct endpoint configured - objects.dreamhost.com and not the CDN URL. Also double-check the credentials if you're not uploading through the control panel.
If you're still having trouble, create a support ticket with some more details and we'll help you figure it out.