It certainly can be used as a non-interactive login, but it's just using stored credentials that you could have used for an interactive login.
Generally, we just create a user (usually a ___domain user) that has permissions to send the mail, and could be used for an interactive login, but the user is never used for anything except the database mail.
The user doesn't have to be given permission to log onto the SQL Server box itself, just to authenticate to the mail server to send mail.