The final set of services to monitor are those on the compute node. Here, you can make sure a couple of services are running and add the ping from the section you just finished. Start with the generic service status check for these services:

neutron-openvswitch-agent
openvswitch
neutron-ovs-cleanup
openstack-ceilometer-compute
openstack-nova-compute

Then add a service configuration to Nagios that will run the ping command to check your tunnel connectivity:

define service {
check_command check_nrpe!check_ovs_tunnel
host_name compute
service_description OVS tunnel connectivity
use generic-service
}

As you can see, this is just an NRPE check command that will execute a ping from the compute node to the network node.