They do accept the dining plan. When we were there (March 9) we were charged one credit per person, but the price points and level of service ABSOLUTELY justify signature status so I wouldn't be surprised if it does end up as a two-credit choice eventually.
By the way, it was one of the best meals of our stay and I wouldn't hesitate to recommend it highly. They offer several non-alcoholic specialties for kids/minors on the plan, and the ones my kids tried were excellent. The arancini was perfect, and the layered pasta dish I had was fabulous. The only tiny, minor complaint I have is that the chicken in my DD's chicken parm was a bit too crispy-fried to work in the dish - it was pounded to a nice thinness but the too-crunchy breading took away from the overall enjoyment. And the place was nearly empty, I think because people just don't know that they do accept the dining plan yet (I got conflicting answers depending on where I looked on the website, and decided just to walk up and ask since we were at Disney Springs anyway).