It's not entirely clear whether you mean to ask about TCP or UDP transport here, but I assume TCP since that's how gmetad-gmetad and gmetad-gmond communication is done.
The only security measures are the trusted_hosts
configuration attribute for gmetad and the access control lists that can be specified for gmond's tcp_accept_channel
configuration.
You could perhaps consider a secure tunneled route between the hosts if you're looking to avoid eavesdropping?