What is the purpose/usage of "DBWC_SingleInstanceOnlyRuleFilter"?
This function is being used in the Oracle rules in order to make sure that the alarm would be fired only from the instance or RAC node level and not from the RAC cluster level. the function later calls for another function which makes sure that the alarm won't change its' severity within a given time tolerance (the default is 1 minute).
If you are using a custom rule, then you don't have to use this function if you don't want its functionality.
The prefix DBWC (database web console) is usually associated with the database cartridge.
The function is used extensively in rules related to Database cartridge, and not referenced in Java and O/S cartridge rules.