Hi Ned,
I believe that you are talking about Game On. They are a sports bar that started in Boston. The one in Boston looks into the batting cages at Fenway Park and you can rent the cages out for a party when the Sox aren't in town.
Game On Atlantic City
The Borgata and Trump Marina can be walked to from Harrah's. There's a pathway that goes by the water that you can follow to the Borgata. I think that it's about a 15 minute walk. Getting over to Trump Marina I think is a little trickier, but you're not going to miss a whole lot by missing the place.
IIRC, you can only bring one guest in with you to a Diamond Lounge. Not sure if that's different at the 7* level though. The other premium card holder lounges in AC charge $10 in comps per person for access - again, only you and one guest. I know that I used to be able to bring more than one person into the Chairman's Club at Trump, but I haven't been in there since I was a Signature Card holder. (Trumps equivalent to seven stars.)
Oh, I am surprised that Noahcat or I didn't suggest Chef Volas. It's not a casino restaurant, but one of the most noted Italian restaurants, yet unknown places in the city.
Chef Vola's information
Zagat reviews
Edited to add: For a casual meal, The White House Sub Shop is a must.