class profile::base {
...
  $agent_zbx_templates = ['OS Linux']
...
  include profile::zabbix::agent
}

classes:
  - profile::haproxy

class profile::haproxy {
    $local_agent_zbx_templates = $profile::base::agent_zbx_templates + ['APP HAProxy']
   class {'profile::base':
    agent_zbx_templates => $local_agent_zbx_templates
   }
}

[root@stress1 ~]# puppet agent -t
Info: Using configured environment 'production'
Info: Retrieving pluginfacts
Info: Retrieving plugin
Info: Loading facts
Error: Could not retrieve catalog from remote server: Error 500 on SERVER: Server Error: Evaluation Error: Error while evaluating a Resource Statement, Evaluation Error: Error while evaluating a Resource Statement, Duplicate declaration: Class[Profile::Base] is already declared; cannot redeclare at /etc/puppetlabs/code/environments/production/modules/profile/manifests/haproxy.pp:48 at /etc/puppetlabs/code/environments/production/modules/profile/manifests/haproxy.pp:48:3 on node stress1.lb.dc2
Warning: Not using cache on failed catalog
Error: Could not retrieve catalog; skipping run

:hierarchy:
  - "node/%{::fqdn}"
  - "environment/%{::environment}"
  - ...