Is the Zend_Cache capable of using SASL auth to connect to the memcachier server?
Assuming you're using ZF 1.x, the manual says that Zend_Cache_Backend_Memcached uses the memcache extension, which does not expressly support memcached 1.4.3+'s SASL support.
Indeed, if any PHP memcached library were to ever gain support, it would be memcached, not memcache. Yes, they are different things. The reason for this is the old non-D'd extension uses an older version of the client library than the newer, D'd extension, which uses the new, official library.