As far as I'm aware, No. The Geoserver documentation doesn't elude to the possibility only discussing a single user creation.
Furthermore, when following OpenGeo Suite tutorial on working on creating multiple users, they go through the process of showing how to create a user and then the following steps to create multiple users is the repeat the steps of creating a single user.
Click Add new user again and repeat the above process, creating two new users, private_viewer and private_edit, and associating them with the ROLE_PRIVATE and ROLE_PRIVATEEDIT roles, respectively.
I've search for this capability as well to no avail in other forums, blogs etc...