Try this in an elevated Powershell console:
$command="dfm event delete "; $i=<starting event ID>; while( $i -lt <ending event ID>) { $command += $i; $command += " " ; $i++}; invoke-expression $command
No NetApp PS tools required in this case.
If your range is too great it might hit a maximum line/command length limit in PS, if there is one. I ack'd then deleted about 500 events in one go without a hitch.