There is some truth in that, but they neglect to give the reason why. If you are taking medications to reduce your blood sugar and the dose is based on a typical higher carb diet, suddenly cutting your carbs can make the medication unnecessary or at the very least you will need a much lower dose than you are currently taking. If you continue to take your normal dose along with cutting your carbs, it's possible to wind up with a hypoglycemic reaction.
Moral of the story? Work with your doctor when you are a diabetic switching to low carb to reduce and/or eliminate your medications as your blood sugars drop and they [the medications] become unnecessary.
If you are responsible and work with your doctor in this manner, low carbing for diabetics becomes no more dangerous than it is for anyone else. Take it from someone who's been a Type 2 diabetic for over 12 years and a low carber (now medication-free, thank you) for over 3.