ok : 

define homelinkhost(ensure) {
   file { "$home/$name":
           ensure => $hostname ? {
              host01 => "$ensure.$hostname",
              default => "$ensure"
           }
   }
}

but not : 

define homelinkhost(ensure) {
   file { "$home/$name":
           ensure => $hostname ? {
              host01 || host02 => "$ensure.$hostname",
              default => "$ensure"
           }
   }
}