I just did some basic tests on my local machine. I started memcached as verbose (and not being a daemon so everything would be sent to sysout), and I tested with both configurations
Both "seem to work", in the sense that either with the extra backendOptions or without it the memcache instance was being hit and keys and values were being stored and retrieved.
However, with the extra "backendOptions" I do not seem to get hits on the memcached instance every time (as if it were bypassing the cache sometimes), whether with my syntax it appeared to hit the memcache server every time. I have no idea why that could happen.
So .. both seem to reach memcache somehow. I am sticking to my configuration since that seems more natural.