If the database doesn't exist the dbhash output should have a clear indication of that, possible like this:

{  host: "mci-osx108.build.10gen.cc:20011",
   md5: false, // for compat.
   missing: true, // indication it is missing and doesn't exist
...}

Adding this additional information will allow the test framework to distinguish when a db exists or not on a replica, independent of storage engine impl. Right now we cannot detect some types of replication failures using dbhash.