While ssh_options is a documented option it can never work. If any value is delivered it is just ignored because of a bug in fencing.py.
It can easily be checked in fencing.py:1347, which is:
if "--ssh-options" in options:
When printing out options it does not show --ssh-options. Instead it shows a value device_options with ssh_options as a value. So the condition is never true and ssh_options always get ignored.