There are various sugars (corn syrup, malt syrup, cane molasses) in the Laxatone hairball remedy so that is not good for diabetic cats. Petromalt also has sugars in it (corn syrup first ingredient) so that one is not good for a diabetic cat either.
There are various chewable hairball treats but most of them have a lot of grains in them and grains are high carb, so not a good idea for a diabetic kitty.
Best idea was BJM's and the petroleum jelly (aka Vaseline). It's the main ingredient in the Laxatone.