try this

inventory/group_vars/all

@@ -259,6 +259,7 @@ createrepo: True
 
 # Nagios global variables
 nagios_Check_Services:
+  monitor: true
   nrpe: true
   sshd: true
   named: false

inventory/group_vars/newcloud

@@ -8,6 +8,7 @@ freezes: false
 ansible_ifcfg_whitelist: ['eth1']
 baseiptables: false
 nagios_Check_Services:
+  monitor: false
   nrpe: false
   sshd: false
   swap: false

roles/nagios_server/templates/nagios/hostgroups/all.cfg.j2

@@ -4,7 +4,7 @@
 ## {{ env }}
 
 {% for key, value in groups.iteritems() %}
-{% if groups[key] != [] %}
+{% if groups[key] != [] and hostvars[host].nagios_Check_Services['monitor'] == true %}
 define hostgroup{
        hostgroup_name {{ key }}
        alias          {{ key }}