echoing this, i would take care NOT to rely on DH for backups. keep your own backups.
my only experience of relying on dreamhost for a backup was from an account that was hacked. I got an email on my secondary (non DH) email saying that somone had changed the account's primary email. the first thing they did, of course, was to lock me out of the account. by the time DH verified my identity and restored my access to the account, they had deleted my domain.
DH informed me that because the domain was deleted, they had gotten rid of ALL backups and i was out of luck. it appears that the DH policy is "backups until you need them".
here is a copy of the relevant reply from DH support:
On 10/19/06, DreamHost Sales Team firstname.lastname@example.org wrote:
good luck, and always keep your own backups of your files AND your databases.