There are some services like Neutron with the "ip" metric and Nova with the "memory" and "vcpus" metrics that are published via bus.

Currently, Ceilometer is ignoring those metrics, but the customer should be able to configure it to retrieve them and get them published to sg-core. However, it seems that the TCP scoket does not have events implemented: https://opendev.org/openstack/ceilometer/src/branch/master/ceilometer/publisher/tcp.py#L98