As far as I'm aware, No. The GeoServer documentation does not allude to the possibility, and only discusses 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...
