Do: Refer people?
Don't do: Spam... or you can lose the account and all referral money.
That's not quite true, since a promo code is a one-shot discount. Once it's time to renew, they don't get to re-apply that discount.
You're better off with something like, "Save $xx when you sign up at Dreamhost," which doesn't imply anything other than a one-time discount.
They give you $97 for each referral. If you choose to use a promo code, whatever discount you give comes out of your $97.
There is no limit to how many people can use the code--but each person can only use it once, since it's for new account sign-ups only.
Save up to $96 at Dreamhost with ALMOST97 promo code (I get $1).
Or save $97 with THEFULL97.