I have asked a similar question some time ago, as you can see here:
Supported password hashes by ZCS 7.2 ldap server .
I'm back at it, and after a while searching, i've found this post from 2005 saying that there's no way to change from SSHA:
Migrating Accounts from LDAP with Encrypted Passwords
Is it still valid info ?
Can't I change the default password hash to, say, SHA512; Then when a user change its password through the web interface, the new password is hashed with SHA512 ?