Tanya,
I guess that what you're really asking is whether you can be in ketosis and still not lose weight? I have seen people reporting that. But, as far as the xylitol is concerned, the only think you can do is to try it out for a while and see. If your weightloss stops for a while, then leave it out of your diet and see what happens. Drawing conclusions just over a few days weight hovering is not saying much, since our bodies naturally hovers sometimes, at points for weeks (heck, even months!) without any change in the diet causing it - just because the system needs to "catch up".

Best of luck!

/gil