I have not tested this in a clustered environment. I will get on this and let you know as soon as I can.
this app's webpage says supported version 6.6, but mostly 6.5.1 would be supported i think.
Products: Splunk Enterprise
Splunk Versions: 6.6
Platform: Platform Independent
the general installation instructions -
This is compatible with 6.5.1. The alert should also act like every other alert action in your cluster.