You can resell your space on any plan, but the plan's aren't setup like a CPanel reseller account, if that's what you're used to. Dreamhost wouldn't handle the billing for your customers, though--that would be up to you.
You can add multiple domains, FTP users, shell users, etc...
Here's some info in the DH Wiki about it: http://wiki.dreamhost.com/index.php/KB_/_Sign_Up_/_Reselling
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