I'm going to hazard a guess that nobody is prepared to test diesel for anything. Where there is an event diesel supplied it takes that problem away.
For streamliner you don't have a problem, you can run anything. The class was designed to be wide open.
For truck classes, unlimited diesel truck is also wide open on fuel (5.F.1). For the other diesel classes at El Mirage for example, there is no event diesel that I know of, so it's, ahem, wide open.