zend_cache is just a front-end for things like memcache isn't it ?
If you plan on using something in memory such as memcache for the zend_cache object, then by all means use the zend_cache object if that's what you're comfortable with. You're probably still going to need the cron job to trigger the script using the zend_cache object on a schedule though.
If you're just going to use a flatfile back-end for the zend_cache object, you might as well just do your own thing and leave out the loading/instancing of the object though. Unless you plan on moving to something like memcache in the future, then it would be better to go with the zend_cache if that's something you're already comfortable using.
Then again, maybe I'm missing something. From what I understand though, zend_cache and cron aren't exactly related technologies functionality-wise.