Multiple Kafka brokers behind a single OpenShift service?
Yes, you can. HAProxy is purpose built to balance any TCP or HTTP connection. My old company used to run every component of Kafka with HAproxy.

Here is a whole project dedicated to running auto-scaling Kafka in Docker using HAproxy: https://github.com/pozgo/docker-kafka

You can even see their HAproxy config here where they specify the broker check (port 9092): https://github.com/pozgo/docker-kafka/blob/master/haproxy.cfg