800 plus member directory & MailChimp or Mandrill?

A local business organization would like us to upgrade their website to WordPress which won't be a problem.
They want a searchable "Member Directory" whereby the members will be uploaded via csv file on a monthly basis. We can do this with Connections Pro plugin but...
We also need this list of members on an email list so when blog posts are made, emails are sent.
I don't want to manage this via another import say to MailChimp but an email solution via Mandrill may work if the email list is managed locally???
Do we just import the users as WP users and use a directory plugin and email plugin which uses Mandrill?
I'm trying to find a WPMU way to do this but cannot seem to put it together in my mind.
Any thoughts / ideas would be appreciated.