You really should have those plates.
As I understand it the wheels that were intended to use them rely on them for strength in that area, the wheel centers themselves are not as thick as they should be if only flanged nuts were used.
I just saw 4 of those plates on some axles I have sitting around here. If I had any extra I'd send them, but I don't right now.
What I'm trying to say is I really think you need and want the plates, and they are out there and easy to find; go find some.
Grigg