It automatically will keep the 1:1 aspect ratio even if you select a 16:9 or 16:10 resolution or whatever. As long as the assets are available to everyone it's within the rules to use any asset (even if you have to pay for it), but I personally feel that you shouldn't have to waste 6 hours the first day trying to get everything set up just to get the resolution right. This all has been confirmed as ok by the jam admins.