There really isn't a 'diabetic' special foods... There are foods that are best avoid most of the time, which in the main is high sugar content but each diabetic will find that they have to tailor there diet to meet there persona; needs...
I'm assuming that you are replacing sugar with an artifical type sweetner, or something like fractose the main problems as such would be if the artifical sugar deteriated in any way when it is heated to high tempretures!! You can ask the manufacuter if the is a problem when using there product when cooking...
Fractose is classed as a nutral sweetner, that doesn't hit the bloood glucose as normal sugar...
But you will need work out the carb content per piece of fudge or at least 100g of your fudge, so that if an diabetic choose it as a treat item, they would know what they tackling, as I would need to know the carb count, so that I could adjust my dose of insulin for it