dedupe rule using birth date is not working using drupal
This sounds odd since it should not be CMS related. I tested on dmaster - set up a DoB based rule, it worked 

Link is below but will be removed when site next rebuilds in a few hours

https://dmaster.demo.civicrm.org/civicrm/contact/dedupefind?reset=1&amp;action=update&amp;rgid=8

Is it possible you made an error setting up your Rule?