Is it viable to attribute permissions to SQL Server virtual accounts (NT Service\SQLSERVERAgent, etc)?
So, firstly have a quick look through this which explains virtual accounts:

TechNet: Service Accounts Step-by-Step Guide

To answer your questions:

1/ You can't list these virtual accounts in that dialog box, I'm not 100% sure of the reason, but you always need to type them in manually, in your screenshot you also have the active directory domain listed, you would never see them in here as they are local accounts.

2/ You can't add permissions on files/shares on another machine by finding these accounts, as they live only on the machine that you installed SQL server on (NVOSIB-1C in your case).  These accounts though can access resources on the network, but they do so in the context of the machine account of the server.

So, an example would be you have NVOSIB-1C with SQL Server installed and NVOSIB-Filer with a share on it that you want the SQL Server account to be able to access.

What you would do in this situation is to add the machine account of the SQL server to the permissions on the file share, you can do this just by assigning the account DOMAINNAME\NVOSIB-1C$ the permissions you want and then as the virtual account accesses the network in the context of the machine it lives on, it would have permission to do so.

Obviously this limits your ability somewhat to assign permissions, as anything running on NVOSIB-1C that authenticated in the context of the server would now have access to the share, if this is a concern, you can do one of 2 things:


Use standard domain service accounts for the SQL Server services, you then need to maintain passwords etc for these, but it makes assigning permissions somewhat easier.
Set up a managed service account in AD, this has the advantage that the local accounts have in that you don't need to worry about passwords, and also the advantage that you can see and manage them centrally in AD like a normal account, the main disadvantage is that you need to have the managed service account created before you install SQL server, so in your case you would have to reinstall to take advantage of this.