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I would say try it on a small batch of something and see how it reacts. I have only used it as an ingredient for baking and it does fine. I am very courious to see what happens. I may have to buy a bag and try it out to see what it does.
I see one person has used it and said it seems to make no difference.
I am diabetic and do not have much of a problem with the rub and sauce, the amount you are using on the meat is not really enough to make a huge difference, in my experience anyway. I'm on an insulin pump, so just adjust a little. In the sauce your probably getting just as much if not more carbs and sugar from all the ketchup. Maybe try 50/50 mix of splenda to sugar. Would be anxious to hear how it works out.
Splenda makes a brown sugar blend that should work (I have not personally tried it). Do note that if the recipe calls for 1 cup of regular brown sugar, you use 1/2 cup of splenda brown sugar, etc.... So cut the amount of splenda brown sugar in half from regular brown sugar.
If you go to the splenda website and read about their brown sugar it is clearly made to be used in baking products which are cooked a higher temperatures that we smoke meat at. This would reduce the calories from carbohydrates in half and keep the sweetness the same. Seems like it would work just fine IMO.