[Plugin: Register Plus] Question before use!

I am wanting to use register plus but I have several websites that use the same database users. I am using the following code:

define(‘CUSTOM_USER_TABLE’, ‘wp_users’);
    define(‘CUSTOM_USER_META_TABLE’, ‘wp_usermeta’);

    to wp-config.php in Secondary WordPress root.
    ——————————
    Changed

    $this->cap_key = $wpdb->prefix . ‘capabilities’;

    to

    $this->cap_key = ‘wp_capabilities’;

    in capabilities.php in wp-includes of Secondary WordPress install

Now my question is if register plus work across the domains/subdomains or will it be individual to each site?

Does Register Plus work with wp_user, wp_usermeta and wp_capabilities or does it have it’s own database settings?

Is there another alternative?

Thanks In Advance [TIA]