I disrecommend doing this: unlike with Cydia, the App Store's customer lists belong to the store and are hidden to the vendor, so you are unable to service your customers via multiple channels without confusion. What will eventually happen is that the user who makes a purchase with one will attempt to use the other to download it, and being unable to do so will complain that they are being charged twice. As jailbreaks become harder over time, some users are always decaying back to stock, and these people will then just be lost customers to you, angry and bitter that they did not use the App Store in the first place. For this reason I am not 100% certain I'd even accept more such paid cross-listed products.
A few things to remember: Cydia is not about "apps"; if you are trying to list an "app" in Cydia for payment and you are not a recognized Cydia developer or from a country that I know hates Apple, I tend to give you a funny look and request more information. If you have something that looks like it was actually rejected from the App Store, you will get a lot of scrutiny, and you should be prepared to be rejected from being sold via Cydia as well. (If you want to list something for free with Cydia you can do so on your own repository: you don't eed to obtain anyone's permission for that.) Things that are designed for Cydia are "extensions" or "daemons" and thereby have entirely different models and goals than software available in the App Store.
