To be clear, if EI (I think you meant EI) has checked your bags to RSW, you will not reclaim and drop them at EWR because, as you note, you have precleared CBP at DUB. However, if you are on separate tickets (I'm presuming one ticket because otherwise not a connection) and EI has not checked through to UA, the bags will be delivered as standard domestic bags and you will then take them and check them in with UA.