Beth:
You could integrate directly with LDAP, actually, and only allow in users tagged with some group or attribute that you deemed fit. OWF's security is "pluggable", meaning you can connect it with a variety of backing authentication and authorization stores. See https://github.com/ozoneplatform/owf/wiki/OWF-7-Configuring-OWF-Security for an explanation of how it works and what to do to configure your auth and auth handshake. Then start with the sample plugins in the owf-security zip file that distributes with OWF. Also consult the https://github.com/ozoneplatform/ozone-security project on GitHub to catch any fixes or tweaks in examples since your bundle came out...
If you're managing users with groups, such that their dashboards, etc, are granted them through their group affiliations, not sure why you need to preload? Otherwise, there's no provided means or manner to do a bulk load of users. We've seen folks build scripts / tools for loading dashboards and widgets: perhaps you could extend the things they're doing there. See if this thread helps...