To answer your first question -> When you grant a specific user permissions to a site, they are added automatically to the hidden User Information list.
As far as an Active Directory group -> The group gets added to the hidden User Information list, but the user does not get added until they access the site. (As an example, I granted an AD group permissions to my site & only the AD group showed up in the hidden User Information list)
As far as the Role group -> After testing on my machine, I can confirm that neither the role group, nor the members get automatically added to the hidden User Information list when you grant permissions.
Also -> this site gives a little more information on the hidden list: