It may not be in group policy directly.
Two approaches: build an ADM Administrative
Template file to create the correct registry entry
and setting.
Perform the option setting from a batch file but
since this one isn't available in the command
line directly either you would end up performing
a registry change (RegIni.exe or Reg.exe).
Either way you have find the setting in the registry.
But this setting is the default and only those users
with enough self-reliance to change the setting
will be viewing hidden files (I would be more
likely to turn ON viewing hidden files.)
