If plaintext passwords were stolen, either the attacker modified the code of the website to prevent pre-transmisssion hashing, or passwords were not salted before they were hashed, so the attackers just brute forced a rainbow table.
SSL wouldn't be of any help. Hashing in the client and authenticating the hash == storing passwords in clear text.
To be honest, it is a little less bad than storing clear passwords because at least a leak wouldn't allow an attacker to screw users who use the same password on different sites. But in what concerns your server, it is the same.