I got your email and decided to add more comment here, because it might help others.....
The real questions is who you paid. If you paid dreamhost directly and used a promo or referral code during registration then you most likely have your own dreamhost account. In this case your information is private. This is the official affiliate program. http://www.dreamhost.com/affiliates/
If you paid another individual or company, they probably just created a granted you privledges to their dreamhost account. Dreamhost doesn't really support this as part of it's referral programs. What the functionality exists for is so that a developer that wants to give his clients full access to their files/databases etc can do so. In that case it's obviously assumed that both of you have access to the areas.
To answer the specific question you asked via email, if the second example here is true, there is no way to prevent the account owner from accessing your files and databases etc. Get your own dreamhost account instead.