Members are a custom post type, so if you use an importer that can import to custom post types, and map the extra fields my plugin creates to the appropriate post_meta fields, then, yes, you can do a mass import. Although I haven’t tried it with the Member Directory, I’m a big fan of WP All Import for importing huge #s of products into WooCommerce (products are a custom post type that WooCommerce creates).
http://www.wpallimport.com/