Is there to way to check heartbeat of 12.52 Policy Server from network load balancer just like checking keep-alive on Secure Proxy Server?
You can monitor the listening ports of the Policy Server. To illustrate quickly,on Linux, you can run :
let's say Policy Server IP 192.168.1.1
# nmap 192.168.1.1 -p 44441-44444
If the Policy Server is up and running, you'll get the output as :
PORT STATE SERVICE 44441/tcp open unknown 44442/tcp open coldfusion-auth 44443/tcp open coldfusion-auth 44444/tcp open unknown
Nmap done: 1 IP address (1 host up) scanned in 0.07 seconds
So depending of the loadbalancer you run, you might also check those ports availability. Add monitoring of the port 44445, if you have configured the Policy Server as central oneview monitoring server too.
I hope that helps,
Keep in mind, using nmap or any other socket testing mechanism (telnet) will only tell you if the TCP port is listening. Just because the port is listening does not mean the backend application (Policy Server) is actually processing traffic.