The lounges are for everyone.
We just back from a trip to WDW and we were staying at the GF and had our own car. One night driving back from AK, my wife wanted to Dole Whip so I went to pull into the Poly. The guard there said I couldn't get in unless I had a reservation at one of the restaurants there. He said even if it was a mobile order at Cap't Cook's and then cancel that order once inside.
I thought he was joking but he wasn't. He allowed me to sit at the gate and place a mobile order. Then he allowed me into the parking lot at the Poly where I then cancelled that mobile order and enjoyed our Doe Whip at Pineapple Lanai.
So, it would depend on which resort lounge you are thinking about going to and then figure out how to get on grounds.