My site is undergoing a brute force login attack. My

My site is undergoing a brute force login attack. My hosting company sent me some instructions to limit the login to the wp-admin and not the wp-login.php. (show below)

My questions.
1. will this help block the hackers for brute force?
2. will this work on a multisite since there are several domain names attached with domain mapping.

Dynamic IP address access, limit by referer

If your IP address changes, or you have a very large amount of possible IPs you're connecting from, you can protect your WordPress site by only allowing login requests coming directly from your domain name. Simply replace example\.com with your own domain name

Currently the brute force attack that is taking place relies on sending direct POST requests right to your wp-login.php script. So requring that a POST request can only come from your domain name, ensures a normal human login attempt instead of an automated bot doing it.

<IfModule mod_rewrite.c>
RewriteEngine on
RewriteCond %{REQUEST_METHOD} POST
RewriteCond %{HTTP_REFERER} !^http://(.*)?example\.com [NC]
RewriteCond %{REQUEST_URI} ^(.*)?wp-login\.php(.*)$ [OR]
RewriteCond %{REQUEST_URI} ^(.*)?wp-admin$
RewriteRule ^(.*)$ - [F]
</IfModule>