Could you please help me understand if the regex for line break in HF/Indexer is the same as the Event_Breaker in a universal forwarder? Also, if Event_Breaker is defined, is it still recommended to give Line Break in heavy forwarder or Indexer?
Yes to both questions, EVENT_BREAKER requires the EVENT_BREAKER_ENABLE flag, it helps the universal forwarder know when it can change to a new server listed in outputs.conf when the autoLBFrequency or autoLBVolume is reached, without this setting the forwarder will wait for the file that is monitored to stop updating for a period of time before making the switch to a different backend server in the outputs.conf list.
The above setting makes no difference to the indexer/heavy forwarding tier which is parsing the data (except in a few edge cases on the UF).
Therefore you want both, the LINE_BREAKER is still required if you have SHOULD_LINEMERGE=false and you want a multi-line event.