An event like the STP I really don't care what kind of a bike is ridden or if a cyclist wants to hang on to a car, or draft another cyclist or paceline (which I have done and the STP literature encourages riders to learn how to do it safely.) It's not a race. There are no prizes. Yes, you get a t-shirt/jacket... you pay for it and it shows up in your mailbox a few days before the ride.
An e-bike rider is going to have to have his own support and extra batteries to complete a ride like the STP. For an e-bike like mine, to ride on full assist (no throttle... don't have one) for 200 miles, I would need 7-8 batteries. On level one assist (which is actually more difficult than riding my carbon fiber bike) I would need about 4 batteries. The batteries are $1200 each. It's not an option that I would even consider in a distance event like the STP. However, if someone chooses to do something like that, I still think they have accomplished an amazing thing. Even if they full-throttle an e-bike (20 mph is the limit) that means they are going to be sitting on a bicycle saddle for a minimum of 10 hours. If it is legally classified as a bicycle, and those types of bicycles are not excluded from an event... nobody should judge or care. If you complete a distance event on your carbon fiber sub 15 lbs bike and you draft in a paceline, should the guy that rode solo on his Walmart bike with nobby tires disapprove of your "accomplishment?"