KV Store can be utilized on SHP - HOWEVER - replication does NOT happen, as the Search heads are unaware of each other. In fact, KVStore is a 6.2 feature, and 6.2 deprecates SHP. So IMHO, I would suggest to start fresh with a SHC and then use KVStore. It will make your life way easier.
The description from server.conf seems telling me it's possible on SHP.
I'm not sure what should be here. FQDN? Or should match with general/serverName in server.conf
replication_host = <host> * In search head pooling, this host value is a requirement for using KV Store. * This is the address on which a kvstore will be available for accepting remotely.
Check out dgladkikh's answer here: http://answers.splunk.com/answers/231043/how-to-configure-and-distribute-kvstore-in-a-splun.html#ans...
The replication_host needs to be set to a name that can be resolved by your DNS from the other members of the replica set.