There are some types of linking that can be a misrepresentation, and that is clearly described as being "not allowed".
I'd be a little careful of interpreting "You're welcome to use whatever images or text links you'd like to link back to us, " so literally as to mean that you don't have to follow the rest of the stated rules.
http://www.dreamhoststatus.com/2006/12/29/rewards-policy-update-dreamhost-trademark-usage/ contains additional information you might find relevant:
"Gaining referrals through misrepresentation, improper use of DreamHost intellectual property (ie. DreamHost trademarks and copyrighted material) or impersonation of DreamHost personnel is strictly prohibited and can result in loss of accrued Rewards and/or removal from the program."
If you have a specific question about this, you are far better off asking support directly than relying on information you receive here, as we are all just customers like yourself.