Hi,
Are you referring to the WordPress general setting “Anyone can register”?
That setting is for enabling/disabling the wp-register screen, it does not affect UM registration form because it is assumed if a sites install a plugin with front-end registration form, that the site wants users to register via UM registration.
If UM registration was tied to that setting then it means that the wp-register method becomes open but websites using UM do not want users to register via wp-register but rather only via UM registration form.
If you don’t want users registering via UM registration form, there is a simple fix for this which is to remove the UM registration page from front-end of your site.
Thanks