I am creating an universal application (run on iPad and iPhone). I want to know if I am not create nib file for iPhone then is this possible that my application is rejected?
If you have a .xib that you're using for both iPhone and iPad, there's nothing inherently wrong with that. I don't think you'll get rejected just for that.
But if your single .xib contains the main window and doesn't automatically resize to full screen -- i.e. only receives touch events in a 320x480 frame -- that could get your app rejected, since your app would have a malfunction when run on the iPad's 1024x768 screen.