Welcome to Flyertalk me4him, and welcome to the Lounges forum.
I appreciate this question straddles two areas - airside access and lounges - but we try to discourage cross-posting in Flyertalk, otherwise it will get very difficult to find key information. I have a feeling that you can use the airside buses since you are arriving domestically into EWR, but I'm sure someone based in NYC will be able to clarify that shortly.
CWS/mod