If I apply to UPenn under the M&T dual degree program but I am not accepted, is it possible that I can be considered for another Dual Degree program I am interested in as a backup?
I do not believe so. Also, NETS is a single major in SEAS not a dual degree.
No, there is no such option with the application form. If you were rejected by M&T, you would be considered for your 2nd choice school, Either Wharton, or Engineering.
You can apply for a dual degree program after you get in.