You’ll get access to the same control panel as the rest of us, so I’m not sure what messages you’d see without signing up for hosting.
Here’s the rewards section of the panel: https://panel.dreamhost.com/index.cgi?tree=home.rew
I take it you didn’t have to enter any payment info, choose a domain, etc… right? Even if you accidentally signed up for hosting somehow, you could cancel it without any hassles if you don’t want it.
Maximum savings promo code: MaxSavingsAtDH