You can totally order food and drinks from the free chairs. We did it on Monday, June 9 and like I said, my server that day actually voluntarily walked up to us twice over 2 hours, as opposed to our experience the day before when we paid $150+tax to sit in a rented cabana for 3 hours (we left an hour early because we were so fed up and hungry and didn't want to wait another hour to order food to be delivered to the cabana).
On Sunday, DH was chasing down multiple people just to put in an order when we had rented the cabana. I contacted Disney to suggest that both the waiter and the cabana attendant be given more training because it was a terrible experience. DH spent the entire 3 hours in the cabana and the only time someone approached him (versus him getting up off the lounger to walk around and find someone) was when they came to tell him (after he had approached them) they couldn't find our waiter either or they just found him and he'd be over shortly. No one ever voluntarily came up to ask, "Would you like to order anything?"