Dear Sango,
You are right. If the splenda and sugar alcohols are being eaten and the stix show you are in ketosis then they are not causing a rise in blood sugar and are not interfering with weight loss.
They can cause cravings for sweets but have a minimal impact on blood sugar levels. If they did, they would be a hell of a class action lawsuit on behalf of diabetics !!
Another reason sugar alcohols can stall you is an increase in calories
http://atkins.com/helpatkins/faqs/faqslow/index.html
Slow Weight Loss and Plateaus
FAQ 1-10 of 10
Could eating Advantage bars be impeding my weight loss?
This varies by individual. If you have reached a plateau and are not losing weight, try omitting the bars until weight loss resumes. Alternatively, you could exercise more to burn the extra calories or try eating only half a bar. Remember, each bar contains approximately 220 calories and these added calories could be affecting your overall weight loss. The controlled carb way of eating has an advantage over low-fat diets in that you can take in more calories and still lose more weight, but don’t regard that as a license to overeat.

Check out his site for more info. It looks like you shoud either eat less sugar alcohols or exercise more to get through a stall. There are so many reasons the weight loss is slow on this plan. I found I had to exercise consistently to lose any weight. It cant be overdone really. And otherwise it can be supplements that get you out of a stall. There is a good tips and stalls sub-forum on this site, you should check out. A few weeks ago a email from atkins center was posted in there regarding slow weight loss that went into some detail as to staying within specific portion recommendations and other things I found enlightening.

Good luck and the best thing is you are eating healthy although I know the hell of just wanting to lose weight fast, and waiting and waiting so just know you will get through this!