I was just wondering that no matter how hard you try their will be some overlap between what you mention in your resume, various sections of the online app and the essays.
Personally, I do not like to repeat information but sometimes you just cannot help. For example if in your resume you have mentioned, I do XYZ for organization ABC. In the online app you would also say something similar and shades of it will also be reflected in your essays.
I like the Wharton approach to be the best, "don't ask for a resume at all". I guess it is only then that the online application makes much more sense and adds value, rather than forcing the applicants to repeat info.