Ad Sharing & AdSense

[setting up the ad sharing plugin]

Is it correct that each one of the bloggers in my WPMU community has to have their own Adsense account in order to participate in shared ad revenue, if that is what I am using?

If so, how do they go about getting an Adsense account, if they only "website" they have is the blog in my community? Hope that makes sense!

Thanks.