John, I think that you have it backwards. Nas replicates the results of reading the alarm2 messages.
Preprocessing operates on the alarm messages before anything else gets to them.
And preprocessing isn't part of the "disable auto operator" checkbox on nas.
So if you have preprocessing, you need to have it set up on all the nas probes and expect it to operate on the alarms regardless of the HA state.
The flow would be something like:
Alarm happens on hub B
alarm enrichment on B reads alarm message and applies preprocessor script to it
alarm2 is published back onto the bus and written to the nas database
replication picks up the new entry to the nas database and forwards to hub A
Hub A stores entry to its database and evaluates AO profiles
relevant AO profiles fire.
At least this is what I observe happening in my environment.
-Garin