Referral programs are allowed on Kickstarter. This means project creators can offer incentives, such as discounts or physical goods, to motivate backers to get the word out about their campaign.
As a campaign creator, it is no different than hiring a marketing firm for a percentage of your overall campaign earnings and having them spend money on your behalf.
Other key rules:
Contests remain prohibited. That means you can't structure referral programs like a contest where backers compete for rewards or participate in drawings.
You're welcome to work with third party referral programs (such as Kickbooster) however when talking about your referral program, Kickstarter doesn't want you to mention the third party you are using (i.e. don't say Kickbooster). Promote your referral program in a tasteful manner on your project page and updates.
Make sure that you have a system in place to track and manage your referral program, and to process and fulfill rewards (that's where Kickbooster comes in - we take care of everything for you!)
For more information we suggest reading Kickstarters FAQs.