Rich, you probably don't have something configured properly. There is no problem with pay later and user creation. You must, of course, enable the user creation option in the DT Register configuration. If you have upgraded, make sure you set this and re-saved the config. If you have it set, but no user is created, submit a ticket.
Rich, sounds like you don't have the latest build. The initial release of 2.6.7 didn't use the auto user registration when profile integration was set to NO. That was fixed and released as 2.6.7a. Check your list of installed components for your version number. If it just says 2.6.7, you need to update then you'll be all set.