Password Field

No, there’s no option because there’s no option in Multisite.

Go look at yourdomain.com/wp-signup.php and you’ll see the same thing. The plugin does not ‘customize’ the signup page in any way, just makes it so you can embed it on different pages.

In theory any way in which you could add it to the normal page using filters would work here as well, but I’ve not tried it.