If I put ios 6 beta on my iphone can I still develop and submit updates for my app on ios 5?
What iOS version you put on your phone doesn't matter. The important thing is, that you can only submit apps using a non-beta version of XCode (the one on the Mac App Store). You can't submit an app to the App Store using the beta version of XCode that is available on the developer portal (and which you need to develop iOS 6 apps) along with iOS 6.