so taking this apart it looks like the unique IP OR dreamhosters.com subdomain means that you have moved the DNS for the domain away from dreamhost.
You obviously want to avoid the unique IP if possible because that's an extra $4.00/month. I also wouldn't be crazy about the idea of using the dresmhosters.com domain as part of a production website on another domain.
Depending on how your DNS is managed, the angle I would take is to have a subdomain like media.domain.com or upload.domain.com hosted via dreamhost while the main domain points elsewhere.
There isn't enough information in your post to get specific tho....