Yup, even though KS will take a cut, it's worth getting those people who will pay to do it through KS. It's a very strong signal on your KS campaign page if by the time the buzz hits that you have 25% of your money already there, you'll convert way more than if you only had say 5%. Social proof is a huge factor in sales. The KS campaigns that are are successful and haven't use this technique are generally outliers.