There is no argument that fiber is beneficial for a diabetic. The problem is that many foods that are high in fiber are also high in carbohydrates. Prime examples are whole grains and legumes. Which are great for high-carb low-fat vegans. However, low-carb high-fat diabetics need to get fiber from low-carb sources, such as chia seeds, flaxseed, psyllium husks, and non-starchy fibrous vegetables.

A High-Fiber Diet Helps You Lose Weight and May Fight Cancer
https://www.atkins.com/how-it-works/atkins-blogs/colette-heimowitz/a-high-fiber-diet-helps-you-lose-weight-and-may-fight-cancer

Grains, beans, nuts, and seeds
http://www.diagnosisdiet.com/food/grains-beans-nuts-and-seeds/

More Evidence That a High-Fiber Diet Can Curb Type 2 Diabetes
http://articles.mercola.com/sites/articles/archive/2015/06/08/fiber-may-lower-diabetes-risk.aspx

The Problem with Grains and Legumes
http://www.amymyersmd.com/2014/03/the-problem-with-grains-and-legumes/