Adding ssl option and setting it to true or false appears to always make it true.

$ ruby test.rb
D, 2015-03-31T11:40:38.213094 #13756 DEBUG – : MONGODB | Adding mowgli:27017 to the cluster. | runtime: 0.0021ms
D, 2015-03-31T11:40:38.215200 #13756 DEBUG – : MONGODB | COMMAND | namespace= admin.$cmd selector={:ismaster=>1} flags=[] limit=-1 skip=0 project=nil | runtim e: 1.9538ms
D, 2015-03-31T11:40:38.215249 #13756 DEBUG – : MONGODB | SSL_connect SYSCALL returned=5 errno=0 state=SSLv2/v3 read server hello A | runtime: 0.0017ms