I wouldn't do it. Being that it's a shared server, there's not much shielding it from other activities on your same webserver, or any other DreamHost server other than a username and a password. Even if it's encrypted, compromised encrypted information is a problem, especially since credit card numbers follow a fixed format. Someone with lots of time has a good chance of brute forcing a crack.
When I've wanted to accept credit card payments, I use PayPal and put a link on my own page for the payment.