I should have posted an update on this thread with what we found earlier today. Blueridge is exactly right, as the software is reading the file, it will only pull in races it thinks it doesn't already have. If it finds a match, it assumes you're simply doing a participant sync and it will add/update the participants in the existing race.
There is value in being able to re-import an entire .evt file to sync the participant list for a current or upcoming race, however I did update the software today so that when it's looking for matching races it will only look for races with the same name and a scheduled start date that is "today" or some time in the future. So with the next update, if you import a Hytek .evt file that has the exact same race name of an older race in ART, it will still create a new race and associate the participants with it as expected. :)