Currently we have only implemented the CMS User Administration with Membership Services.
You can easily set your own Membership, Role and Profile providers, making the appropriate changes in the Web.config file:
<roleManager defaultProvider="YourRoleProvider" enabled="true">
<add name="YourRoleProvider" type=.../>
<add name="YourMembershipProvider" type=... />
<add name="YourProfileProvider" type=.../>
Please let us know if you have some feedback/suggestions about User Administration in Sitefinity 3.0 as we intend to improve it till the official release.