Just so you know, you can't really nest a host group into another host group. You can have a host being part of multiple host groups, but I had a fellow IRC Nagios member point me to your article confused about how to nest host groups.
Correct me if I'm wrong, but the only directives you can use in a host group are: hostgroup_name, alias, and members (meaning hosts). You can't put a hostgroup name into the members category either, because when you do the config check, nagios doesn't like it.
Just something to perhaps correct, if I'm indeed correct. Thanks!