Users who click FB Connect can be automatically registered with a Joomla account and immediately logged into your site. You can test that functionality on this site.
As for DT Register, we don't currently have a profile plugin for integration with that extension. We currently have plugins for JomSocial, Community Builder, K2, Kunena, and a few others. We do have some guides on how to create profile plugins, if you have a developer who can create that functionality for you.
You can look at our
Facebook profile import to Joomla
page for a list of the fields that can be imported to any extension, with the right profile plugin.
Without a profile plugin, the user account can still be created in Joomla automatically with the user's full name and email address. DT Register can then use that information to start their profile for them. That would work immediately, and while it may not be everything you want, it's a great starting point as it still streamlines the registration process a bit.
Hope that helps answer your question,
Alex
DT Register
