I'm actually at the lounge in DUB right now. I booked SEA-DUB and DUB-LIS on two separate tickets. The check-in agent at SEA tagged my bags to LIS and provided both BPs. Upon arrival into DUB, I provided the lounge attendants both of my BPs and they just looked at it, jotted down my connecting flight on a piece of paper, then invited me in.
Not sure how nice the showers are at the PP lounge next door but the showers here were pretty awful.