I've always played with the Cisco ACS on Windows boxes, but I purchased a Cisco ACS Appliance / Solution Engine sometime ago. I didn't know at the time PING was disabled by default. Here is how enable ping response from the appliance / solution engine
The Cisco Secure ACS Solution Engine does not respond to pings like a normal, Windows−based Cisco
Secure ACS server.
The failure of the Cisco Secure ACS Solution Engine to respond to pings is the result of the rule set applied to the CSA installed on the appliance. In order to allow ping on your ACS Solution Engine, you need to disable the CSA.
This can be done via the System Configuration > Appliance Configuration menu.
There is an option to disable or enable the CSA. If you disable this agent, you can then ping the appliance