In addition to the fact that only root has access to the command line and the webUI, a user named root on the network does not have any special access to shares. Using root to access network shares is just the same as using some other user that you haven't created in the webUI. That is, root is only a guest for network share access.
There are users you create through the webUI, but root is not one of those, though it does allow you to set the root password in the webUI.
Users you create in the webUI are the only users that can be given restricted access to shares on the network. Everybody else will only have guest access. Guests have full access to public shares, and readonly access to secure shares.
So there is no point in using root to access network shares, though if you do happen to use that username on the network to access shares, it gets treated as any other guest.
Unraid isn't intended to be a general purpose, multiuser linux. It is a stripped down, customized slackware linux designed as a NAS OS with docker and VM hosting.