Support for ssl has been added to the develop branch. Check it out and let me know if anything's broken :)
A style note: since the server URIs use the standard Mongo connection string format, I'm expecting the query param style rather than the ruby opt style names. For example, you would use connectTimeoutMS rather than :connection_timeout.
Genghis (.rb) currently only supports replicaSet, connectTimeoutMS and ssl. All queries are done with safe, so that option doesn't make sense to set at the server level. I don't want to support slaveOkay (at least until Genghis supports read-only users, but possibly ever). If you need to connect to a slave, just connect directly to the slave...
The rest of the options seem to be unsupported at the connection level by the Ruby driver, so they'll take a bit more to integrate.