GA and DL will provide you lounge access if traveling in J (likely in KE lounges)....though you may have to seek out a pass from a GA agent.
GA ground handling and services absolutely suck, so good luck getting you bag checked all the way through if you are flying the same route home (I have failed multiple times from DPS...having to reclear security in ICN). DL can check you through all the way there.
However, GA J on-board service is among the best you will find. A very enjoyable flight.