Yes, I have popped in there for a beer to go on occasion. We use the TIW card and we get a 20% discount there which is always nice.
If you are in the backlot then don't forget to stop in to "High Octane". It is a full service bar and it is outside, but you can find some shaded seating nearby on those hot days.
The bar area at the Tune-in Lounge gets insane in the afternoon when people crowd in there waiting to get called for their dinner reservations. I have seen families sitting at the bar with their kids eating dinner since they could not get a seat in the restaurant (50's Prime Time). The bar is not where I would seat my child for dinner, but it is not my child.
Try a Dad's Electric Lemonade. (Dad whips up an electrifying blue drink with Bacardi rum, Skyy vodka, blue curacao, sweet and sour mix and Sprite) It tastes great on those hot days. Below is a link to the available Adult beverages available in DHS. For the Tune-in Lounge, just scroll to the bottom and go to page 2 and it gives you a list of draft beers and specialty cocktails.
http://www.partythroughtheparks.com/hs/