We have an existing Zend Framework site hosted at ourdomain.com and a wordpress blog at blog.ourdomain.com
We want to migrate the blog into the site at ourdomain.com
I wrote an open source library that might solve your problem called Vulnero that allows you to run your Zend Framework application inside WordPress. Your routes get handled by your app, everything else goes to WordPress. Can even render your views in your WordPress template if you like. Integrates authentication, database connections, all that. Source is on GitHub or you can read the documentation at http://www.vulnero.com/.