I've used Emerald Reserve in October and December and both times I used the $20 entertainment coupons. No problem. Both were collected when I drove to the kiosk. I've been using emeral reserve the last 2 visits because I wanted a full size car and my July trip I arrived to an empty EA lane and had an intermediate car asigned to me. Before that I had always had good choices in the EA to choose from.
I believe, like the other posters, that you do have to visit the counter if the coupon is an upgrade coupon.