Yes, the refillable mug station is right there in Trail's End. When I was there recently, I went in to fill my mug and there were a few tables of folks eating lunch. I'm interested in what the new menu was all about so I was trying to take a peek at what they had. I did notice that one of the families had their mugs on the table.
I just don't see a waiter or waitress saying "sorry, you can't use your refillable mugs, you have to order a drink"....but then again, with Disney locking up their soda machines, they might...