I have never tried to make sushi with pudding rice and I can understand that some have tried with the lack of sushi rice. For pudding rice is a short grain rice as sushi rice however, I think they are slightly shorter.
I do not believe that pudding rice can be used for sushi. It is another type of rice and the texture when they are cooked is not the same as the pre-cooked sushi rice.
As a sushi chef I have cooked sushi rice over the years with various brands and quality. Even within the sushi rice is a big difference in how the rice grains react when they have been washed, boiled and cooled down.
Please read more about sushi course for beginner where I talk more about sushi rice.
Zoë has lectured and held sushi courses for A. P. Moller – Maersk, Hugo Boss Nordic, Novo Nordisk, Novartis, Velux, Gorrissen Federspiel, Beierholm revision, Elbek & Vejrup and many more.