Thats odd that you wouldn't be able to replicate. I don't see why not, to be honest. I haven't quite addressed our backup plans just yet. I was going to do SQL replication between two servers, but I guess not now.
If that is the case, I am already planning on converging two local SQL databases for our two servers onto one server and I'll just make daily/nightly backups of it and restore as needed. I still haven't decided on the type of backup yet - either database-level or export/file-level.
Atleast with the shared database, I'll be able to move users from one server to the other w/o issues. I just really do not see why you cannot do an active-passive replication though.