Sorry, but EI Transatlantic J Pax DO have access to UA Lounges where on a single ticket.
It just appears to be limited primarily to those locations where EI is pushing a UA connections over B6 - I have used this benefit at ORD myself, but believe its available at SEA, LAX, SAN & MSP - not sure why not at EWR - but it may have been extended there too. You can use pre or post transatalntic.
Pretty sure this is hidden somewhere on the EI website