I had not looked at GasBuddy.com until just now. It seems to me that most of the diesel stations that I looked at around CO/NE/IA were automotive diesel stations that we could not get into. Maybe I am doing something wrong.
No, you're not doing anything wrong. The site is user-contributed data, and most users are in cars or light trucks, so the database is mostly automotive stations. That said, the truck stops are usually in there, too, but there is nothing to set them apart other than recognizing the name of a truck stop chain.
That said, we buy fuel at automotive stations all the time, and if we can get in to them, it's hard to imagine you'd have any trouble. You might have to unhook your toad before rolling in, though. But the savings are huge; when we just filled in Las Vegas (at an automotive Arco station), fuel was a full 25 cents less per gallon then at the cheapest truck stops in the area. We put in 180 gallons, so we saved $45. That would seem to me to be worth unhooking the toad at a nearby shopping center. It's also worth the extra 20 minutes or so to fuel from the smaller automotive nozzles.
As they say, YMMV.