The ones that could figure it out (before/without seeing the panel), could figure it out before they signed up by checking your domain.
Most people probably don't care what you do, as long as they're getting what they paid for from you. Actually, most probably wouldn't understand what you were talking about even if you told them.
Plus, if you offer a service above & beyond what DH does, it doesn't really matter if they know who DH is. (web design, SEO, third party script support, freebies/discounts, etc...)
A reseller is never going to compete with the big boys on price/space/bandwidth... but there are plenty of other reasons to choose a host. The ones that would leave over one or all of those 3 things would probably be doing you a favor.
If someone tells you they're leaving for Dreamhost, don't forget to give them a referral link/promo code.
Save up to $96 at Dreamhost with ALMOST97 promo code (I get $1).
Or save $97 with THEFULL97.