zf-doctrine-multi-manager is for simple handling of multiple entity managers in your Zend Framework application. Although this is not necessary for your actual application – since you know the entity managers – 3rd party modules don’t know them.
There was also the possibility to read the actual doctrine config (doctrine->entitymanager) and use an array_keys, but reading an other module’s config should be avoided from my perspective.
With this module there is now a published interface to get the EntityManagers in your modules extending doctrine.