Hi Craig,
I just realized this was for Opt In Email and not for Dynamic Registration so let me try it again.
The Opt In Email extended fields are separate from the DNN User accounts because the module is designed so that one can subscribe to newsletters without necessarily creating an account.
However, you can integrate Dynamic Registration with Opt In Email so that all accounts created via Dynamic Registration will automatically be subscribed to an Opt In List and carry with it the first name, last name and email. DNNHero offers a video tutorial on Integrating DotNetNuke Registration with an Email Newsletter Subscription module.
http://www.dnnhero.com/Videos/tabid/59/EntryId/241/Integrating-DotNetNuke-Registration-with-an-Email-Newsletter-Subscription-module-part-1-of-2-Video-221.aspx
Hope that helps!
Candace