Hi David,
Yes, you can make one ADFS server as a backup for another one.
I have run a search on this requirements, and I found some links on the question for your reference :
Questions about ADFS and Single Sign On (SSO) with Office 365 for Education:
http://blogs.technet.com/b/educloud/archive/2011/09/23/questions-about-single-sign-on-sso-with-office-365-for-education.aspx
ADFS High / Geo Redundancy:
http://social.technet.microsoft.com/Forums/en-US/winserverDS/thread/80220b1c-d024-4f51-af9e-f38c4fe19c31
Fault tolerant sites with federation service:
http://community.office365.com/en-us/forums/613/t/11651.aspx
ADFS Redundancy between two separate sites:
http://community.office365.com/en-us/forums/613/t/64787.aspx
Help me make by ADFS 2.0 setup more redundant:
http://arstechnica.com/civis/viewtopic.php?f=17&t=1184407
Global ADFS Logon Options with Office 365:
http://blogs.perficient.com/microsoft/2011/10/global-adfs-logon-options-with-office-365/
In addition, you can also post a thread on ADFS forum for more professional information about the issue:
http://social.msdn.microsoft.com/Forums/en/Geneva/
For the password sync issue, I want to confirm whether you want to sync the password from the AD to the cloud. If this is the case, at present, the feature is not available.
Thanks,
Linda Wang