Hybrid apps are partially native and partially web apps. Like the natives, they should be downloaded through a store app (such as Android’s Google Play and Apple’s App Store), stored on the main screen of the device and can enjoy all the features of the device (camera, GPS, accelerometer, gestures etc). As web apps, they can be HTML5-based and displayed via an in-app browser, having some or all of the content uploaded from the web.
You will have a very similar codebase in general, however, there will be peculiarities for each platform, as for example the code for UI. The UI on Android is different from IOS, so you will have to separate the UI codebase, or Assets, if you prefer.
What we can take advantage of in both versions, is how you will treat the data coming from your WS, via Restful, SOAP, RTC, etc. This codebase can be the same, you will treat the data with the Pattern you choose and reuse this code on both mobile platforms.
We can then reach the conclusion that the code will be partially reused and partially redone, but it is more advantageous than developing natively, because in the latter case there is no reuse of any code, thus being slower to develop.