Frank Bültg writing on WPengineer has posted an interesting article: how to “Create Users Automatically In WordPress” which could be used to create a bridge to other systems.
Frank Bültg has created the code so that it creates a user as soon as you go to the backend. For this you can use the functions.php of your Theme or a Plugin, after that you can take out the code.
“To keep the Bridge maintain and up to date and users synchronized, there is a function for updating a user – wp_update_user.”
Full article” http://wpengineer.com/2054/create-users-automatically-in-wordpress/