It looks like the US Customs and Border Protection website quotes Preclearance wait times at DUB between 2-3:30pm so it's likely the DUB-SEA flight is eligible. That being said, even if Preclearance is closed, why connect in the US (esp. ORD where you have to deal with temporary shuttle bus between terminals) which adds at least two hours to your overall journey and you will have to re-check your luggage?