It is recommended to have a native widescreen version because most judges (if not all) are on HDTV ,but I dont think its a requirement. If it'll be a big problem to convert to 16:9 then just check resolutions and add borders or stretch backbuffer when necessary.
Anyway the game should *work* at least on 1280*720 and 1920*1080 settings. Having support for more resolutions is a plus ,and watch out for the 10-20% outer borders of the screen ,some displays cannot display it ,avoid rendering important text/stuff there.
Hope this helps.