You can reduce the amount of history the EMS probe stores but currently can not disable this all together.
set the following in the setup section for EMS Probe
storage_retention_days = 1
enable_transaction_logging = false
this will tell EMS to only store ONE day of alarm history.
Deactivate EMS and delete everything from the Nimsoft/probes/service/ems/db/ folder and then activate the probe.
This should cause the probe to only store alarms for the current day and one previous day.