I believe that the documentation referred to might be insufficient and incorrect.
In particular I think that data_engine needs to be running on the HA standby. It will detect that it is a standby and is supposed to play nice with the data_engine on the primary.
Also, there are probes like discover, ugs, id_server, etc. that will need to be controlled as they in some way dependent on data_engine.
A decent "cookbook" for HA setup on the current 8.31 product would be nice to see as no one seems to be able to provide a definitive answer.
-Garin