“Not yet” because there IS a ruby-shadow rpm available in fedora (see: https://bugzilla.redhat.com/show_bug.cgi?id=240008).

So we only need to download and rebuild it:
wget http://download.fedora.redhat.com/pub/fedora/linux/extras/6/SRPMS/ruby-shadow-1.4.1-6.fc6.src.rpm
rpmbuild --rebuild ruby-shadow-1.4.1-6.fc6.src.rpm


Once we have that rebuilded rpm we can install it on all our puppet-clients. Off course we are not going to do this manually but use puppet for it .
If you have a local repository you can just add the package, but this is not yet the case for my setup so we need some extra rules.
Here is a snippet of puppet manifest:

class ruby-shadow {
   package {
      "ruby-shadow":
         ensure   => installed,
         provider => rpm,
         source   => "/tmp/ruby-shadow-1.4.1-6.i386.rpm",
         require  => file["/tmp/ruby-shadow-1.4.1-6.i386.rpm"],
   }

   file {
      "/tmp/ruby-shadow-1.4.1-6.i386.rpm":
         source => "puppet://puppetmaster/files/ALL/tmp/ruby-shadow-1.4.1-6.i386.rpm"
   }
}

class users {
   include ruby-shadow
   user {
      "root":
         ensure   => present,
         name     => "root",
         password => "SomeAlreadyEncryptedPassword";
   }
}

With this code it will require 2 runs of the puppet client. Even if you add a require in the user section for the ruby-shadow package 2 runs are necessary. Don’t know if this is a bug or a feature…